I had a similar problem. I thought I would add my resolution.
In visual studio, the telerik controls came up with a box that said that it could not load assembly...blah blah
I tried to remove the Telerik.dll form the gac using gacutil.exe, but was told that other applications were dependent on it. Finally i did the following steps:
Disabling the Assembly Cache Viewer
WARNING: The following steps involve modifying the Windows Registry. If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. The author as well as Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.
If you want to disable the Assembly Cache Viewer and see the GAC in all its naked glory within Windows Explorer, you can set
HKLM\Software\Microsoft\Fusion\DisableCacheViewer [DWORD] to 1. (these instructions were found on: http://www.codeproject.com/KB/dotnet/demystifygac.aspx)
This allowed me to see the actual files in the assembly folder. I did a search on this folder for Telerik.
This listed several files and folders. I deleted them.
When I opened Visual Studio, I could see all my controls just fine.
I then went into the registry entry I added above and set the value to 0.
Looking at my assembly folder showed that it reverted to the default view.
Everything works fine now.