Edit: My apologies, it appears this is a known issue and is being worked on.
I'm having a bizarre issue with the RadTabControl related to the design interface in Visual Studio 2010. Every time I try to edit or view the events of the RadTabControl, it crashes the design interface forcing me to reload. I am getting an exception of MS.Internal.Validate+ValidationFailure each time it fails. Whenever I can actually click on the "Events" tab in the properties window, it continues to show the properties. This seems to be related to the Q1 2011 release as I was not having this issue before. Reinstalling the Q1 release did not fix the issue.
The application compiles and debugs without any problems even with the event still defined, so the problem seems purely on the VS side. Any idea what could be causing this?