RadControls for .NET v2.0 were introduced as of Q4 2005 and are not supported for use with the .NET 4.0 framework, as noted on Telerik's .NET Support
page. This version of the controls is nearly 7 years old and it has never been tested in the .NET 4.0 framework. Therefore, they cannot be supported.
I would highly recommend that you upgrade your RadControls to the latest version and then retest your application. This will allow you to get support for all of your issues going forward.