Thank you for contacting us and sorry for the delayed reply.
This is a known issue, which we recently fixed and the fix will be included in our next major release - Q2 2012. It is observed when Telerik.WinControls.Themes.Office2010Black.dll is added to the GAC by VSExtensions upgrade wizard. Prior to 2011 Q3 Release, version 2011.3.11.1116, the mentioned assembly was needed in GAC, but after that release it is not. That's why, fixing this issue goes through removing this dll file from Global Assembly Cache.
Here are the steps to follow for fixing the toolbox issue:
1. Close all Visual Studio instances and run Visual Studio Command Prompt
2. Run the following command: gacutil -u Telerik.WinControls.Themes.Office2010Black
3. Start Visual Studio and launch the Toolbox configurator
4. Choose the distribution you would like to upgrade to.
5. Add Telerik.WinControls.UI.Design.dll assembly to GAC using the gacutil.exe
Regarding the error messages, I hope they will be gone, once the toolbox issue is fixed.
I hope this will help.
the Telerik team