You could try removing all the information from the assembly declaration except the assembly name. This means that you need to remove the Version, Culture, and the PublicKeyToken from the assembly declaration.
If that does not help you resolve the issue, please share your Web.Config file content.
Additionally, you could try to close all the opened instances of Visual Studio and then clear the content of these folders:
- C:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files
Give these suggestions a try and check whether the issue is resolved.
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed