User Controls in User Controls?

I have the follow set up and it is throwing an error "Unhandled error loading module" ... is there some trick to this that I don't know?
I have a project A that uses controls from project B (project B is just a project with all my user controls used through out other modules).  project A uses user control 1 from project B with out any issues at all - great.  But then I wanted to add user control 2 to user control 1 and that is when I get my error.  In fact I don't even have the user control 2 in user control 1, just when I put the register part into user control 1 is when it all falls over.

For reference how I'm calling the user controls:
In Project A, Page A:
<%@ Register TagPrefix="MyControl" TagName="ControlOne" Src="~/DesktopModules/ProjectA/ucControlOne.ascx" %>
In User Control 1:
<%@ Register TagPrefix="MyControl" TagName="ControlTwo" Src=<see below> %>

OK for the source on the second register I've tried the following
~/DesktopModules/ProjectA/ucControlTwo.ascx
ucControlTwo.ascx
../DesktopModules/ProjectA/ucControlTwo.ascx
c:\inetpub\www\dnn311\DesktopModules/ProjectA/ucControlTwo.ascx

This should work right?  What am I doing wrong?  Thanks for any help in advance!