Without having the code you experience this issue with it will be impossible to find a solution. Is that exception thrown in your test methods or do you get an exception in the Test Studio source code? If latter, can you share the stack trace and the test code with us?
the Telerik team
Check out the Test Studio roadmap
to find out more about the new performance testing functionality coming in our R2 2011 release this September!
Have you looked at the new Online User Guide
for Telerik Test Studio?