I have built a site that used forms authentication.
Logging in works initially but after like 20 or 30 secs, I get logged out. I suspect it is because the cookie is getting lost somehow.
Any reasons why this may happen? 
 
<?xml version="1.0"?>
<!-- 
    Note: As an alternative to hand editing this file you can use the 
    web admin tool to configure settings for your application. Use
    the Website->Asp.Net Configuration option in Visual Studio.
    A full list of settings and comments can be found in 
    machine.config.comments usually located in 
    \Windows\Microsoft.Net\Framework\v2.x\Config 
-->
<configuration>
	<configSections>
		<sectionGroup name="system.web.extensions" type="System.Web.Configuration.SystemWebExtensionsSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
			<sectionGroup name="scripting" type="System.Web.Configuration.ScriptingSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
				<section name="scriptResourceHandler" type="System.Web.Configuration.ScriptingScriptResourceHandlerSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="MachineToApplication"/>
				<sectionGroup name="webServices" type="System.Web.Configuration.ScriptingWebServicesSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
					<section name="jsonSerialization" type="System.Web.Configuration.ScriptingJsonSerializationSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="Everywhere"/>
					<section name="profileService" type="System.Web.Configuration.ScriptingProfileServiceSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="MachineToApplication"/>
					<section name="authenticationService" type="System.Web.Configuration.ScriptingAuthenticationServiceSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="MachineToApplication"/>
					<section name="roleService" type="System.Web.Configuration.ScriptingRoleServiceSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="MachineToApplication"/>
				</sectionGroup>
			</sectionGroup>
		</sectionGroup>
		<sectionGroup name="n2" type="N2.Configuration.SectionGroup, N2">
			<section name="host" type="N2.Configuration.HostSection, N2" requirePermission="false"/>
			<section name="engine" type="N2.Configuration.EngineSection, N2" requirePermission="false"/>
			<section name="database" type="N2.Configuration.DatabaseSection, N2" requirePermission="false"/>
			<section name="edit" type="N2.Configuration.EditSection, N2" requirePermission="false"/>
			<section name="templates" type="N2.Templates.Configuration.TemplatesSection, N2.Templates" requirePermission="false"/>
		</sectionGroup>
	</configSections>
	<appSettings>
		<add key="Telligent.Glow.MultipleFileUpload.FileManagerProvider" value="CommunityServer.Components.MultipleUploadFileManager, CommunityServer.Components"/>
		<add key="Telligent.Glow.MultipleFileUpload.UploadHandlerUrl" value="~/multipleupload.ashx"/>
	</appSettings>
	<connectionStrings configSource="connectionStrings.config"/>
	<n2 xmlns="http://n2cms.com/schemas/configuration/v3">
		<!-- If you install a database from scrach you'll need to insert some required pages. 
			This can be done by the web based installer located at http://yoursite/install/edit -->
		<host rootID="716" startPageID="717" multipleSites="false">
			<!-- Make sure to enable wildcard mapping to use empty extension -->
			<web extension=".aspx"/>
			<outputCache enabled="false" duration="10"/>
		</host>
		<engine>
			<assemblies>
				<!-- These assembly declarations are not necessary unless you run in medium trust -->
				<add assembly="N2"/>
				<add assembly="N2.Security"/>
				<add assembly="N2.Edit"/>
				<add assembly="N2.Templates"/>
			</assemblies>
			<!-- Update email to receive error reports -->
			<errors action="Email" mailTo="" mailFrom="noreply@yourdomain.com"/>
			<!-- Globalization requires you to create additional start pages with a language -->
			<globalization enabled="true"/>
			<!-- Will ping the site to prevent it from sleeping -->
			<scheduler keepAlive="false" interval="10"/>
		</engine>
		<!-- Other flavours: SqlServer2005, SqlServer2000, MySql, SqLite, SqlCe, Firebird -->
		<database connectionStringName="SiteSqlServer" flavour="SqlServer2005" caching="true" cacheProviderClass="NHibernate.Caches.SysCache2.SysCacheProvider, NHibernate.Caches.SysCache2"/>
		<edit>
			<!-- Set checkInstallationStatus to false to disable redirect to install page -->
			<installer checkInstallationStatus="true"/>
			<uploadFolders/>
		</edit>
		<templates masterPageFile="~/Themes/ChubNelson/Common/template.master"/>
	</n2>
	<system.web>
		<!-- 
            Set compilation debug="true" to insert debugging 
            symbols into the compiled page. Because this 
            affects performance, set this value to true only 
            during development.
        -->
        <webServices>
            <protocols>
                <add name="HttpGet"/>
                <add name="HttpPost"/>
            </protocols>
        </webServices>
		<compilation debug="true">
			<assemblies>
				<add assembly="System.Core, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
				<add assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
				<add assembly="System.Data.DataSetExtensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
				<add assembly="System.Xml.Linq, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
			</assemblies>
			<expressionBuilders>
				<add expressionPrefix="CurrentItem" type="N2.Web.Compilation.CurrentItemExpressionBuilder, N2"/>
				<add expressionPrefix="CurrentPage" type="N2.Web.Compilation.CurrentPageExpressionBuilder, N2"/>
				<add expressionPrefix="StartPage" type="N2.Web.Compilation.StartPageExpressionBuilder, N2"/>
				<add expressionPrefix="Code" type="N2.Web.Compilation.CodeExpressionBuilder, N2"/>
				<add expressionPrefix="HasValue" type="N2.Web.Compilation.HasValueExpressionBuilder, N2"/>
			</expressionBuilders>
		</compilation>
		<!--
            The <authentication> section enables configuration 
            of the security authentication mode used by 
            ASP.NET to identify an incoming user. 
        -->
		<authentication mode="Forms">
			<forms name=".CommunityServer" protection="All" timeout="600000" loginUrl="login.aspx" slidingExpiration="true"/>
		</authentication>
		<customErrors mode="Off" defaultRedirect="~/error.htm">
			<error statusCode="404" redirect="~/error-notfound.aspx"/>
		</customErrors>
		<pages validateRequest="false" enableEventValidation="false" autoEventWireup="true" pageBaseType="CommunityServer.Components.CSPage, CommunityServer.Components">
			<controls>
				<add tagPrefix="n2" namespace="N2.Web.UI.WebControls" assembly="N2"/>
				<add tagPrefix="n2" namespace="N2.Templates.Web.UI.WebControls" assembly="N2.Templates"/>
				<add tagPrefix="CSControl" namespace="CommunityServer.Controls" assembly="CommunityServer.Controls"/>
				<add tagPrefix="CSBlog" namespace="CommunityServer.Blogs.Controls" assembly="CommunityServer.Blogs"/>
				<add tagPrefix="CSForum" namespace="CommunityServer.Discussions.Controls" assembly="CommunityServer.Discussions"/>
				<add tagPrefix="CSMail" namespace="CommunityServer.MailGateway.MailRoom.Controls" assembly="CommunityServer.MailGateway"/>
				<add tagPrefix="CSMedia" namespace="CommunityServer.MediaGalleries.Controls" assembly="CommunityServer.MediaGalleries"/>
				<add tagPrefix="CSDynConfig" namespace="Telligent.DynamicConfiguration.Controls" assembly="Telligent.DynamicConfiguration"/>
				<add tagPrefix="CSHub" namespace="CommunityServer.Hubs.Controls" assembly="CommunityServer.Controls"/>
				<add tagPrefix="CSMessage" namespace="CommunityServer.Messages.Controls" assembly="CommunityServer.Messages"/>
				<add tagPrefix="CSWiki" namespace="CommunityServer.Wikis.Controls" assembly="CommunityServer.Wikis"/>
				<add tagPrefix="TWC" namespace="Telligent.Glow" assembly="Telligent.Glow"/>
				<add tagPrefix="TWC" namespace="Telligent.Glow" assembly="Telligent.Glow.MultipleFileUpload"/>
				<add tagPrefix="CP" namespace="CommunityServer.ControlPanel.Controls" assembly="CommunityServer.Web"/>
				<add tagPrefix="asp" namespace="System.Web.UI" assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
				<add tagPrefix="asp" namespace="System.Web.UI.WebControls" assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
			</controls>
			<tagMapping>
				<add tagType="System.Web.UI.HtmlControls.HtmlForm" mappedTagType="N2.Web.UI.WebControls.RawUrlForm"/>
			</tagMapping>
		</pages>
		<httpHandlers>
			<remove verb="*" path="*.asmx"/>
			<add path="*.n2.ashx" verb="*" type="N2.Web.AjaxRequestHandler, N2"/>
			<add verb="GET" path="Utility/redirect.aspx" type="CommunityServer.Components.Redirect, CommunityServer.Components"/>
			<add verb="GET" path="aggbug.aspx" type="CommunityServer.Components.HttpHandler.AggBugHandler, CommunityServer.Components"/>
			<add verb="GET" path="avatar.aspx" type="CommunityServer.Components.HttpHandler.AvatarHttpHandler, CommunityServer.Components"/>
			<add verb="GET" path="vcard.aspx" type="CommunityServer.Components.HttpHandler.VCardHttpHandler, CommunityServer.Components"/>
			<add verb="GET" path="r.ashx" type="CommunityServer.Components.HttpHandler.TinyUrlHttpHandler, CommunityServer.Components"/>
			<add verb="GET" path="weblogsubscription-confirmation.ashx" type="CommunityServer.Blogs.Components.WeblogSubscriptionConfirmation, CommunityServer.Blogs"/>
			<add verb="GET" path="threadsubscription-confirmation.ashx" type="CommunityServer.Blogs.Components.ThreadSubscriptionConfirmation, CommunityServer.Blogs"/>
			<add verb="GET" path="cfs-file.ashx" type="CommunityServer.Components.FileHttpHandler, CommunityServer.Components"/>
			<add verb="GET" path="cfs-filesystemfile.ashx" type="CommunityServer.Components.FileSystemFileStorageHttpHandler, CommunityServer.Components"/>
			<add verb="GET" path="resized-image.ashx" type="CommunityServer.Components.ImageFileResizerHttpHandler, CommunityServer.Components"/>
			<add verb="GET,POST" path="multipleupload.ashx" type="Telligent.Glow.MultipleUploadFileHandler, Telligent.Glow.MultipleFileUpload"/>
			<add verb="*" path="*.asmx" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
			<add verb="*" path="*_AppService.axd" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
			<add verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" validate="false"/>
		</httpHandlers>
		<httpModules>
			<add name="n2.initializer" type="N2.Web.InitializerModule, N2"/>
			<add name="CommunityServer" type="CommunityServer.CSHttpModule, CommunityServer.Components"/>
			<add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
		</httpModules>
		<trace enabled="false" requestLimit="40" localOnly="true"/>
		<sessionState mode="Off"/>
		<siteMap defaultProvider="PublicSiteMap">
			<providers>
				<add name="PublicSiteMap" type="N2.Web.PublicSiteMapProvider, N2" startPageIsRoot="true"/>
			</providers>
		</siteMap>
		<membership userIsOnlineTimeWindow="15" defaultProvider="CommunityServerSqlProvider">
			<providers>
				<clear/>
				<add name="CommunityServerSqlProvider" type="CommunityServer.ASPNet20MemberRole.CSMembershipProvider, CommunityServer.ASPNet20MemberRole" connectionStringName="SiteSqlServer" enablePasswordRetrieval="false" enablePasswordReset="true" requiresQuestionAndAnswer="false" requiresUniqueEmail="true" passwordFormat="Hashed" applicationName="dev" description="Stores and retrieves membership data from the local Microsoft SQL Server database" maxInvalidPasswordAttempts="999" passwordAttemptWindow="999" minRequiredPasswordLength="6" minRequiredNonalphanumericCharacters="0"/>
			</providers>
		</membership>
		<roleManager defaultProvider="CommunityServerSqlProvider" enabled="true" cacheRolesInCookie="true" cookieName=".CSRoles" cookieTimeout="60000" cookiePath="/" cookieRequireSSL="false" cookieSlidingExpiration="true" createPersistentCookie="true" cookieProtection="All" maxCachedResults="1000">
			<providers>
				<clear/>
				<add name="CommunityServerSqlProvider" type="CommunityServer.ASPNet20MemberRole.CSRoleProvider, CommunityServer.ASPNet20MemberRole" connectionStringName="SiteSqlServer" applicationName="dev" description="Stores and retrieves roles data from the local Microsoft SQL Server database"/>
			</providers>
		</roleManager>
		<profile defaultProvider="CommunityServerSqlProvider" enabled="true">
			<providers>
				<clear/>
				<add name="CommunityServerSqlProvider" type="CommunityServer.ASPNet20MemberRole.CSProfileProvider, CommunityServer.ASPNet20MemberRole" connectionStringName="SiteSqlServer" applicationName="dev" description="Stores and retrieves profile data from the local Microsoft SQL Server database"/>
			</providers>
			<properties>
				<add name="commonName" type="string"/>
				<add name="birthdate" type="DateTime"/>
				<add name="gender" type="int" defaultValue="0"/>
				<add name="dateFormat" type="string" defaultValue="MM-dd-yyyy"/>
				<add name="publicEmail" type="string"/>
				<add name="language" type="string"/>
				<add name="webAddress" type="string"/>
				<add name="webLog" type="string"/>
				<add name="webGallery" type="string"/>
				<add name="signature" type="string"/>
				<add name="signatureFormatted" type="string"/>
				<add name="location" type="string"/>
				<add name="occupation" type="string"/>
				<add name="interests" type="string"/>
				<add name="msnIM" type="string"/>
				<add name="yahooIM" type="string"/>
				<add name="aolIM" type="string"/>
				<add name="icqIM" type="string"/>
				<add name="enablePostPreviewPopup" type="System.Boolean" defaultValue="false"/>
				<add name="enableEmoticons" type="System.Boolean" defaultValue="true"/>
				<add name="timezone" type="System.Double" defaultValue="0"/>
				<add name="fontsize" type="int" defaultValue="0"/>
				<add name="bio" type="string"/>
			</properties>
		</profile>
		<!--<trust level="Medium" />-->
		<!-- 
		========================
		Anonymous Identification
		========================
		anonymousIdentification configuration:
			enabled="[true|false]"                            Feature is enabled?
			cookieName=".ASPXANONYMOUS"                       Cookie Name
			cookieTimeout="100000"                            Cookie Timeout in minutes
			cookiePath="/"                                    Cookie Path
			cookieRequireSSL="[true|false]"                   Set Secure bit in Cookie
			cookieSlidingExpiration="[true|false]"            Reissue expiring cookies?
			cookieProtection="[None|Validation|Encryption|All]"  How to protect cookies from being read/tampered
			domain="[domain]"                                 Enables output of the "domain" cookie attribute set to the specified value
			-->
		<anonymousIdentification enabled="false" cookieName=".ASPXANONYMOUS" cookieTimeout="100000" cookiePath="/" cookieRequireSSL="false" cookieSlidingExpiration="true" cookieProtection="None" domain=""/>
	</system.web>
	<location path="user/EditProfile.aspx">
		<system.web>
			<authorization>
				<deny users="?"/>
			</authorization>
		</system.web>
	</location>
	<system.codedom>
		<compilers>
			<compiler language="c#;cs;csharp" extension=".cs" warningLevel="4" type="Microsoft.CSharp.CSharpCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
				<providerOption name="CompilerVersion" value="v3.5"/>
				<providerOption name="WarnAsError" value="false"/>
			</compiler>
			<compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" warningLevel="4" type="Microsoft.VisualBasic.VBCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
				<providerOption name="CompilerVersion" value="v3.5"/>
				<providerOption name="OptionInfer" value="true"/>
				<providerOption name="WarnAsError" value="false"/>
			</compiler>
		</compilers>
	</system.codedom>
	<!-- 
        The system.webServer section is required for running ASP.NET AJAX under Internet
        Information Services 7.0.  It is not necessary for previous version of IIS.
    -->
	<system.webServer>
		<validation validateIntegratedModeConfiguration="false"/>
		<modules>
			<remove name="ScriptModule"/>
			<add name="ScriptModule" preCondition="managedHandler" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
            <add name="n2.initializer" type="N2.Web.InitializerModule, N2"/>
            <add name="CommunityServer" type="CommunityServer.CSHttpModule, CommunityServer.Components"/>
		</modules>
		<handlers>
			<remove name="WebServiceHandlerFactory-Integrated"/>
			<remove name="ScriptHandlerFactory"/>
			<remove name="ScriptHandlerFactoryAppServices"/>
			<remove name="ScriptResource"/>
			<add name="ScriptHandlerFactory" verb="*" path="*.asmx" preCondition="integratedMode" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
			<add name="ScriptHandlerFactoryAppServices" verb="*" path="*_AppService.axd" preCondition="integratedMode" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
			<add name="ScriptResource" preCondition="integratedMode" verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
            <add name="n" path="*.n2.ashx" verb="*" type="N2.Web.AjaxRequestHandler, N2"/>
            <add name="u" verb="GET" path="Utility/redirect.aspx" type="CommunityServer.Components.Redirect, CommunityServer.Components"/>
            <add name="a" verb="GET" path="aggbug.aspx" type="CommunityServer.Components.HttpHandler.AggBugHandler, CommunityServer.Components"/>
            <add name="v" verb="GET" path="avatar.aspx" type="CommunityServer.Components.HttpHandler.AvatarHttpHandler, CommunityServer.Components"/>
            <add name="vc" verb="GET" path="vcard.aspx" type="CommunityServer.Components.HttpHandler.VCardHttpHandler, CommunityServer.Components"/>
            <add name="r" verb="GET" path="r.ashx" type="CommunityServer.Components.HttpHandler.TinyUrlHttpHandler, CommunityServer.Components"/>
            <add name="w" verb="GET" path="weblogsubscription-confirmation.ashx" type="CommunityServer.Blogs.Components.WeblogSubscriptionConfirmation, CommunityServer.Blogs"/>
            <add name="t" verb="GET" path="threadsubscription-confirmation.ashx" type="CommunityServer.Blogs.Components.ThreadSubscriptionConfirmation, CommunityServer.Blogs"/>
            <add name="c" verb="GET" path="cfs-file.ashx" type="CommunityServer.Components.FileHttpHandler, CommunityServer.Components"/>
            <add name="cf" verb="GET" path="cfs-filesystemfile.ashx" type="CommunityServer.Components.FileSystemFileStorageHttpHandler, CommunityServer.Components"/>
            <add name="r" verb="GET" path="resized-image.ashx" type="CommunityServer.Components.ImageFileResizerHttpHandler, CommunityServer.Components"/>
            <add name="mu" verb="GET,POST" path="multipleupload.ashx" type="Telligent.Glow.MultipleUploadFileHandler, Telligent.Glow.MultipleFileUpload"/>
		</handlers>
	</system.webServer>
	<runtime>
		<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
			<dependentAssembly>
				<assemblyIdentity name="System.Web.Extensions" publicKeyToken="31bf3856ad364e35"/>
				<bindingRedirect oldVersion="1.0.0.0-1.1.0.0" newVersion="3.5.0.0"/>
			</dependentAssembly>
			<dependentAssembly>
				<assemblyIdentity name="System.Web.Extensions.Design" publicKeyToken="31bf3856ad364e35"/>
				<bindingRedirect oldVersion="1.0.0.0-1.1.0.0" newVersion="3.5.0.0"/>
			</dependentAssembly>
		</assemblyBinding>
	</runtime>
</configuration>
  

 Use 
sessionstate timeout in your config file. More details can be found here at MSDN http://msdn.microsoft.com/en-us/library/ms972429.aspx
--
(Please, Mark as Answer if it Helped)
http://smsohan.blogspot.com

I turned session state mode to inproc and timeout to 20.
I'm still getting the error. 
trying logging in with 
username: testuser 
password: 1234qwer 
click on links and page loads fast and you stay logged in. After about 30 sec of clicking links, they page request time doubles and you get signed out.