I'm glad to hear you've managed to resolve this.
This is expected behavior. In the Visual Studio plug-in you will need to manually rebuild the project every time you introduce changes to the code-behind file. Running the test will also compile it in Stand Alone edition of Test Studio but not in the Visual Studio plug-in.
the Telerik team
for a live 'What's New in Test Studio R1 2011 SP2' event on Tuesday, July 19 at 2pm EST!
Have you looked at the new Online User Guide
for Telerik Test Studio?