To me it sounds like there is something going on with the server setup, and not the application itself. Have you read and followed the instructions in the Add/Remove RadControls to the GAC
documentation article? I'm suspicious regarding the fact that you might have multiple versions of the RadControls on the same server, which could cause some issues with references (an application accidentally looking at the wrong assembly version etc.) that could cause the behavior that you are describing. I would make sure that there is only one version of the RadControls on your server and double-check that everything is all set in the GAC.