Most probably there is some issue with the upgrade of the visual studio extensions. In order to resolve the issue please go to C:\Program Files [or x86]\Microsoft Visual Studio 10.0\Common7\IDE\Extensions\Telerik\Telerik Sitefinity SDK VSExtensions
folder and delete all files. Then reinstall the your Sitefinity installation. Note that if you have already installed the RadControls it is not necessary to reinstall them from the Sitefinity installation as they become a separate download once you initially indicate that you want them.
Please let me know whether the problem still persists.
All the best,
the Telerik team
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