This thread became a bit long one and I'm sorry we were still unable to help.
To my regret haven't come across this exact error before and I can't help with a direct reply.
I'm not sure if I understood the problem in its entirety, but I would suggest a clean setup of the VSExtensions. Here are the steps to do that:
- Close all Visual Studio instances;
- Start a Windows Explorer and navigate to the %localappdata%\Microsoft\VisualStudio\10.0\Extensions folder (on Windows7 and Windows Vista you could paste this to the address bar);
- Check if there is a Telerik folder and delete it if existing;
- Navigate to the C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\Extensions folder and delete the Telerik subfolder;
- Visit the Visual Studio Online Gallery and download the Telerik VSExtensions you would need (Telerik WebUI VSExtensions handle the RadControls for ASP.NET AJAX VSExtensions) to a folder of your choice (e.g. C:\Install);
- Start a Visual Studio 2010 Command Prompt and navigate to the folder you downloaded the VSIX;
- type vsixinstaller /a [VSPackageName],
e.g. vsixinstaller /a Telerik.WebUI.VSPackage.vsix for the RadControls for ASP.NET AJAX VSExtensions, hit ENTER and follow the wizard.
- Start Visual Studio and check if everything will be okay now.
The extensions we published to the Online Gallery are the most recent official ones.
Let me know if that helps.
the Telerik team