Error Creating Control in VS design view

[John]

Is there a way to prevent this? It makes life difficult when you can't use the design view. (see attached)

Note, this happens everywhere in the project.

[Vessy]

Hi John,

The most probable reason for the experienced error could be a previous version DLLs cached in the GAC. This is so, could you verify that  the installation PC was restarted after the installation?

If you have already done it, though, and the problem still exists, there might has been some warnings in the installation wizard, preventing some DLLs to be referred properly. Automated tools may not always produce the expected results, the following manual approach should let you upgrade in a manner of minutes: Upgrade the Version of Your Telerik ASP.NET Controls in 6 Easy Steps

If the controls in your application are registered with their fully qualified name, you have to make sure that they are pointing to one and the same version (probably the latest installed one).

You can find more information about the Global Assembly Cache and how to add/remove dlls from it in the following blog post: Working with Assemblies in the GAC

Regards,
Vessy
Telerik