I am afraid that we are not aware of what would cause such an exception with the RadGridView. In the Exception message I see the problem OnGotFocus of the RadWindow. Have you placed the GridView into a RadWindow? What is the previous version you upgraded from?
It would be very helpful if you could isolate the issue in a demo project. You can check this blog post for a reference on how to isolate a problem in a sample project.
the Telerik team