We managed to reproduce your problem in the following situation: we added the RadControls manually in Visual Studio Express toolbox. Then we uninstalled RadControls. In this situation when you try to drop some RadControl from the toolbox the same exception occurs.
To solve your issue we suggest you to follow these steps:
- Uninstall the RadControls suite
- Ensure that "C:\Program Files\telerik" is removed
- Ensure that there are no dll-s in GAC beginning with Telerik. namespace.
- Remove manually all RadControls from Visual Studio and Visual Studio Express
- Reinstall RadControls for WinForms
Please tell us if this information was useful or we need some additional research.
the Telerik team