I am experiencing the last problem (added per Visual Studio load) in Visual Studio 2010 with the Telerik 2012 Q1 controls. I'm curious, has a fix aside from a complete re-install been discovered yet?
Edit: It seems this is caused by WCF RIA Services. I fixed this by following these steps:
- Uninstall WCF RIA Services.
- Remove toolbox cache: *.tbd files from directory "%USERPROFILE%\Local Settings\Application Data\Microsoft\VisualStudio\10.0
- Remove the "Toolbox" keys from the following registry locations (if present)
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SDKs\Silverlight\v4.0\AssemblyFoldersEx\Ria Services v1.0 Silverlight Libraries
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SDKs\Silverlight\v5.0\AssemblyFoldersEx\Ria Services v1.0 Silverlight Libraries
Hope this helps anyone else having the same issue.