I am sorry for the trouble that you have encountered.
The problem is cause by the VS extensions for RadControls for ASP.NET AJAX not installed properly. To resolve the issue I suggest you to reinstall just the VS extensions which is really easy using the Visual Studio Extension Manager (found under the Tools menu). Here are the steps you need:
- Launch the Extension Manager;
- Locate the Telerik WebUI VSExtensions, uninstall them and restart the IDE;
- Launch the Extension Manager again and switch to the Online Gallery tab;
- Search for Telerik WebUI VSExtensions, install them and restart the IDE;
This should resolve the issue on your side.
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed