AAAARGGGGGGGGHHHHHHHH.....
Ok, the error has been seen quite often...I've checked a lot of forums and all they seem to provide as a solution is to uninstall everything and make sure the latest dll's are in the bin directory of my website.
Here are the files in my bin directory:
AjaxControlToolkit.dll version: 1.0.61214.0
AjaxControlToolkit.pdb version: 
AJAXExtensionsToolbox.dll version: 1.0.61025.0
System.Web.Extensions.Design.dll version: 1.0.61025.61025
System.Web.Extensions.dll version: 1.0.61025.61025

Now, I've done exactly that! and checked all the versions but still the error remains....
Below you see my web.config file

Im not sure about this part in the web.config, but if I remove it I receive a bunch of other errors about the <microsoft.web> section:
    <sectionGroup name="microsoft.web" type="Microsoft.Web.Configuration.MicrosoftWebSectionGroup, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35">
      <section name="converters" type="Microsoft.Web.Configuration.ConvertersSection"/>
    </sectionGroup>


WEB.CONFIG


<?xml version="1.0"?>
<configuration xmlns="http://schemas.microsoft.com/.NetConfiguration/v2.0">
 <configSections>
    <sectionGroup name="microsoft.web" type="Microsoft.Web.Configuration.MicrosoftWebSectionGroup, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35">
      <section name="converters" type="Microsoft.Web.Configuration.ConvertersSection"/>
    </sectionGroup>
    <sectionGroup name="system.web.extensions" type="System.Web.Configuration.SystemWebExtensionsSectionGroup, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35">
   <sectionGroup name="scripting" type="Microsoft.Web.Configuration.ScriptingSectionGroup, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35">
    <sectionGroup name="webServices" type="Microsoft.Web.Configuration.ScriptingWebServicesSectionGroup, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35">
     <section name="jsonSerialization" type="Microsoft.Web.Configuration.ScriptingJsonSerializationSection, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" requirePermission="false"/>
     <section name="profileService" type="Microsoft.Web.Configuration.ScriptingProfileServiceSection, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" requirePermission="false"/>
     <section name="authenticationService" type="Microsoft.Web.Configuration.ScriptingAuthenticationServiceSection, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" requirePermission="false"/>
    </sectionGroup>
   </sectionGroup>
  </sectionGroup>
 </configSections>
 <system.webServer>
  <validation validateIntegratedModeConfiguration="false"/>
  <modules>
   <add name="ScriptModule" preCondition="integratedMode" type="Microsoft.Web.UI.ScriptModule, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
  </modules>
  <handlers>
   <remove name="WebServiceHandlerFactory-ISAPI-2.0"/>
   <add name="ScriptHandlerFactory" verb="*" path="*.asmx" preCondition="integratedMode" type="Microsoft.Web.Script.Services.ScriptHandlerFactory, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
   <add name="ScriptResource" verb="GET" path="ScriptResource.axd" type="Microsoft.Web.Handlers.ScriptResourceHandler"/>
  </handlers>
 </system.webServer>
 <microsoft.web>
  <converters>
   <add type="Microsoft.Web.Script.Serialization.Converters.DataSetConverter"/>
   <add type="Microsoft.Web.Script.Serialization.Converters.DataRowConverter"/>
   <add type="Microsoft.Web.Script.Serialization.Converters.DataTableConverter"/>
  </converters>
 </microsoft.web>
 <connectionStrings>
  <add name="SQLAuth" connectionString="data source=LT1600\SQLEXPRESS;Initial Catalog=Data;User Id=sa;Password=hallow;" providerName="System.Data.SqlClient"/>
  <add name="AdminLink" connectionString="data source=LT1600\SQLEXPRESS;Initial Catalog=Data;User Id=sa;Password=hallow;" providerName="System.Data.SqlClient"/>
  <add name="WebUser" connectionString="data source=LT1600\SQLEXPRESS;Initial Catalog=Data;User Id=webuser;Password=hallow;" providerName="System.Data.SqlClient"/>
 </connectionStrings>
 <system.web>
  <trust level="Medium"/>
  <compilation debug="true" strict="false" explicit="true">
   <assemblies>
    <add assembly="Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
    <add assembly="System.Design, Version=2.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A"/></assemblies>
  </compilation>
  <pages maintainScrollPositionOnPostBack="true">
   <controls>
    <add tagPrefix="asp" namespace="Microsoft.Web.UI" assembly="Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
    <add tagPrefix="asp" namespace="Microsoft.Web.UI.Controls" assembly="Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
    <add namespace="AjaxControlToolkit" assembly="AjaxControlToolkit" tagPrefix="ajaxToolkit"/>
   </controls>
   <tagMapping>
    <add tagType="System.Web.UI.WebControls.CompareValidator" mappedTagType="Microsoft.Web.UI.Compatibility.CompareValidator, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
    <add tagType="System.Web.UI.WebControls.CustomValidator" mappedTagType="Microsoft.Web.UI.Compatibility.CustomValidator, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
    <add tagType="System.Web.UI.WebControls.RangeValidator" mappedTagType="Microsoft.Web.UI.Compatibility.RangeValidator, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
    <add tagType="System.Web.UI.WebControls.RegularExpressionValidator" mappedTagType="Microsoft.Web.UI.Compatibility.RegularExpressionValidator, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
    <add tagType="System.Web.UI.WebControls.RequiredFieldValidator" mappedTagType="Microsoft.Web.UI.Compatibility.RequiredFieldValidator, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
    <add tagType="System.Web.UI.WebControls.ValidationSummary" mappedTagType="Microsoft.Web.UI.Compatibility.ValidationSummary, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
   </tagMapping>
   <namespaces>
    <clear/>
    <add namespace="System"/>
    <add namespace="System.Collections"/>
    <add namespace="System.Collections.Specialized"/>
    <add namespace="System.Configuration"/>
    <add namespace="System.Text"/>
    <add namespace="System.Text.RegularExpressions"/>
    <add namespace="System.Web"/>
    <add namespace="System.Web.Caching"/>
    <add namespace="System.Web.SessionState"/>
    <add namespace="System.Web.Security"/>
    <add namespace="System.Web.Profile"/>
    <add namespace="System.Web.UI"/>
    <add namespace="System.Web.UI.WebControls"/>
    <add namespace="System.Web.UI.WebControls.WebParts"/>
    <add namespace="System.Web.UI.HtmlControls"/>
    <add namespace="Samples.AccessProviders"/>
   </namespaces>
  </pages>
  <httpHandlers>
   <remove verb="*" path="*.asmx"/>
   <add verb="*" path="*.asmx" validate="false" type="Microsoft.Web.Script.Services.ScriptHandlerFactory, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
   <add verb="GET" path="ScriptResource.axd" type="Microsoft.Web.Handlers.ScriptResourceHandler" validate="false"/>
  </httpHandlers>
  <httpModules>
   <add name="WebResourceCompression" type="Microsoft.Web.Handlers.WebResourceCompressionModule, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
   <add name="ScriptModule" type="Microsoft.Web.UI.ScriptModule, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
  </httpModules>
 </system.web>

</configuration>




please mark answers as 'Answered' and post back solutions when you figure stuff out that isnt in the post already.

Hi Peter,
Are you using the Release Candidate of Ajax? If so, then all of the namespaces have changed from Microsoft.* to System.*. You just need to search & replace within your web.config, or, cut n paste from the template one in the Microsoft ASP.NET folder. 
Regards,
Chris
Chris Field - MCP, MCSD 
My Own Limited - Bespoke Software Development

Please Post Detail About this error. Because meet error
 Thank .............
 
Thank you,
IT Manager

Ok I Don't know why it's working now for me but here what i did....
1. Install the latest Asp.NET Ajax
2.Open my web.config in my production server and replace this line 

<add assembly="System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
by 
 <add assembly="System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
It's the same thing but the PublicKeyToken is in capitals....
Save it and browse to my site and bingo!
Hope this help...
 

Thank you
Thank you,
IT Manager

very much thnx, I was searching for hours for this solution!

Did this fix actually work for anyone???
 AJAX 1.0 is working beautifully on my developement machine but when I publish a website to my production server I get:
 Configuration Error 

            

             Description: An
error occurred during the processing of a configuration file required
to service this request. Please review the specific error details below
and modify your configuration file appropriately. 



             Parser Error Message: Could
not load file or assembly 'System.Web.Extensions, Version=1.0.61025.0,
Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its
dependencies. The system cannot find the file specified.



            Source Error: 



            

               

                  

                      
Line 36: 		<compilation debug="true">
Line 37: 			<assemblies>
Line 38: 				<add assembly="System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
Line 39: 				<add assembly="System.Design, Version=2.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A"/>
Line 40: 				<add assembly="System.Web.Extensions.Design, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/></assemblies>

                  
               
            

            


             Source File:  d:\WebSites\Secure\test\web.config    Line:  38
            



            Assembly Load Trace:
The following information can be helpful to determine why the assembly
'System.Web.Extensions, Version=1.0.61025.0, Culture=neutral,
PublicKeyToken=31bf3856ad364e35' could not be loaded.
 
 I have been on Microsoft's "off-shore" support line for two hours.  They walked me through installing "hotfix for issue 915782. ".  After two hours the support technician told me that this hotfix doesn't really fix this problem and if I would like to open another paid support case they would be happy to send this problem to the engineers and research it.  The support tech told me that currently do not have a fix for this problem.
 
I really like the functionallity of AJAX and it would be a great addition to our corporate public website BUT like all Microsoft products I fear I am going to have to wait for AJAX SP1 or AJAX SP2 before it actually works.  With as long as I have been using Microsoft products you think I would know better by now.  Maybe I will try Oracles "Comet" or Suns "Soft Scrub" technology!
 

Do you run the .msi installer on the server?
Steve Marx | ASP.NET AJAX Evangelist | Microsoft Corporation

I meant "did" you run the .msi installer on the server. ;-)
If you didn't, you need to.  (Barring that, you can copy the DLLs into the /bin folder as long as you can configure your app for full trust.)
Steve Marx | ASP.NET AJAX Evangelist | Microsoft Corporation

I am having the same problem. 
 
I am trying to run the AJAX Documentation website. I am trying to follow the readme.htm file. I have followed all of it's instructions. 
I am getting the same error, 
Could not load file or assembly 'System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.

Sorry for my ignorance, but which dll's and into which bin folder?
 
Thanks, Dan R. 
in to code - dr43058

Just copy the System.Web.Extensions.dll into the bin directory of your web application

Where is this file located and what if I don't have it, where would I get, would I get it by the process of installing something or do I need to pull if from somewhere?
 
I have installed:
VB 2005 EE
Visual Web Developer EE
SQL Server Express 2005 EE
Management Studio Express 
 Oh, duh, do I need to install the AJAX control toolkit at this point?
Is that why I don't have a 'Microsoft ASP.NET directory under 'C:/Program Files'?
in to code - dr43058

You need to install ASP.NET 2.0 AJAX Extensions 1.0
http://www.microsoft.com/downloads/details.aspx?FamilyID=ca9d90fa-e8c9-42e3-aa19-08e2c027f5d6&displaylang=en
 

Never mind I just answered my own question, I hadn't installed the extensions yet, that's why 'microsoft asp.net' directory didn't exist or the system.web.extensions.dll file, this is all so complicated, thanks, 
 
Dan Ros. 
in to code - dr43058

Hey there, 
 
One quick thing worth noting is that even AFTER I installed the AJAX extensions, I still got this error. I ended up having to restart the IIS service on the local machine... 

 pack27:
Just copy the System.Web.Extensions.dll into the bin directory of your web application

 This worked fine for me, the reference was going to program files, and those are not on the publish server, so I put those dll's in the bin folder and changed the reference to the dll in my bin.
grz

Hi
 
Please can someone help me out, i'm trying to get it straight in my head what i actually need to do top correct this error.
 I'm getting the same error and after reading the posts it sounds like i need to either (?) install the ajax extensions on my server (which i can't do as i don't have root access or any rights), OR i can copy the .dll files into my bin directory, change the web.config file to point to the dll files in the bin and copy this to my server (please correct me if i'm talking out my @rse) - which is what im now trying to do!
I've tried adding a reference but nothing is added even after i have selected the .dll files, so then i tried to do it manually and copy from C:\WINDOWS\assembly folder straight into the bin, but i cant copy/move the files....what am i doing wrong??
 
thanks
 

Ive been stressing over this exact problem 4 time, till i came across this thread.
All i had to do is copy the system.web.extensions.dll into the bin folder in the server thats all. No need to rewire the config file to point to the bin or anything as it finds it automatically.
 Thanks everyone :))

 i just had the same problem, and all i had to do is copy both the System.Web.Extensions and System.Web.Extensions.Design .dll's into the bin directory of where i am copying the project to.
 this, however, sounds like a bug to me. the dll's are already in the GAC of the target machine, which tells me that these dll's aren't being recognized in the GAC. can we open a work order for this one?
 

hi
just download the extentension from the following link http://www.microsoft.com/downloads/details.aspx?FamilyID=ca9d90fa-e8c9-42e3-aa19-08e2c027f5d6&displaylang=en , install it and cheers
(edited : sorry, i didnot found that this reply has been already made , perhaps browser shows me cached version of page.)
thanks
vishal

hi Oughtsix 
 
actually this problems comes when your run your .net 2.0 application first time which have a reference to this dll , but while installing .net that dll doesn't comes with the part of setup so you have to install the .msi installer (link has been already posted in the thread), that installer installs the dll of the same version with same public key in the gac and update. 
so it is the best practice to run that .msi extention instead of messing around by installing yourself in the gac.
thanks
vishal

i got this issue resolved. I installed ASP.NET 2.0 in the windows Server 2003, and it worked fine.Thanks for that solution.

Thank you for this 

Ok. I had the same problem as this post did so I made the changes, I then rebuilt my solution and republished it to our prod environment and then recieved this error. I searched the web with no resolution to my issue. can some one please help me?! Thank you
Could not load file or assembly 'Microsoft.VisualStudio.ProjectAggregator, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.

thanks to YOU guys  my web site is working(sins i had the same prob)

Somebody please help me fix this error, I am getting the same error. I have installed, uninstallled and reinstalled with the ASPAJAXSourceCode.msi.
I went and checked the GAC after this and I don't see any System.Web.Extensions dll registered with the GAC, so that would make sense why this error is occuring. What is wrong with the installer that it is not registering this dll with the GAC?
Please Help!

I guess the source MSI doesn't appear to register the System.Web.Extensions dll  in the GAC, I had to also run the non source extensions msi to get this registerd in the GAC and that fixed the problem.

Ok, the ASP extensions install did fix the issue for me, and IIS didn't need to be restarted > Everything works fine > 
The link I followed on the server >  
http://www.microsoft.com/downloads/details.aspx?FamilyID=ca9d90fa-e8c9-42e3-aa19-08e2c027f5d6&displaylang=en
Derek Hinch
Senior Developer

Here is what worked for me.
After Installing Ajax .MSI into my development pc, i thought I didn' need to install anything into production server which would have been nightmare downtime etc.
So, all i did was copied 4 .dll into the Bin folder of the site Not the Server itself. They are:
System.Web.Extensions.dll
System.Web.Extensions.Design.dll
AJAXExtensionsToolbox.dll
AjaxControlToolkit.dll (from the Toolkit folder).
The first 3 can be found were you install the Ajax 1.0 in your pc(.msi installation)
 I was compelled to write this to others won't panic like i did.
Thanks for all the earlier posts; they helped.
 
 
 

 Thanks, the problem was that my hosting provider dont have installed the extensions.
 
But now is ready. 

Regards

WOw this helped me ..Just make the PublicKeyToken=31bf3856ad364e35'  CAPITAL and it works 
Thanks .I was banging my head for whole day

 that was the solution I needed. Thanx very much!!!
 

Thank you for this solution, it was just what I needed.

Hi,
 Thanks that reallyt helped be alot !! Saved me hours of search for a stupid lower/uppercase thingy !!
 
Thanks again.

Its simple. Just serach the files eg. System.******** and copy those files into the bin directoy of your website. You shold be good.

 I had the same problem since I opened the Visual Studio for the first time, but when I closed VS and reopened, I didn't get the error. It worked fine. 
Cheers,
Achutha Krishnan

~ No one can do everything, but everyone can do something ~

 That has certainly gotten me past the inability to compile, but now I am getting "Microsoft JScript runtime error: 'Sys' is undefined"....
 I am really close to uninstalling all this AJAX crap.  What a bug filled bunch of bull.  I am burning DAYS on this and cannot demo the application because of a MS bug...
 Could anyone PLEASE help me on this?
 I have VS 2005 and VS 2008 installed and have the same problem in both.  Nothing seems to get me past the "Microsoft JScript runtime error: 'Sys' is undefined" error.  I have installed, uninstalled, CTP, beta, etc. with no luck what so ever.
Please help this extremely frustrated developer.  :)
Thanks in advance,
 
B


 
Bill Myers
Centillion Industries Incorporated
Pittsburgh, PA

This helped me.. thanks Alot :)  

 woony:
 

 pack27:
Just copy the System.Web.Extensions.dll into the bin directory of your web application
 
-Jigzy-

Please remember to click “Mark as Answer” on the post that helps you.

This can be beneficial to other members reading the thread. 

 pack27:
 
It's the same thing but the PublicKeyToken is in capitals....
Save it and browse to my site and bingo!

I found this from 2-Jan-07. It works for me. After an entire afternoon changing permissions etc because only a FULL administrator can install the AjAX kit on my server, and it still not working, I came across this little gem!
How the hell were we supposed to guess that the key was case specific, especially as it works on my dev machine.
Harrumph! 
a louse is not a home, a bug is just a feature

Thanks a lot!
 I also have an application in which I used the ASP.NET AJAX Controls but since the dlls are not on the Server and My Service Provider is not ready to make the favour for me. So this helped me a lot. You have solved one of my greatest problem
 Once Again Thanks a lot!
 

It worked for me, too.
 THanks.
--jdd

This worked perfectly! 
Thanks,
Mike G.

HI. Makesure you have same version in GAC and you are not missing to add refrences of dependent dll .
  
you can play with GAC like this 

http://www.revenmerchantservices.com/ajax/systemwebextensions.html 

Satalaj   :)
 
 

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