I am sorry to hear you are experiencing issues.
That issue could be observed when there is reference to a version of Telerik.Web.UI in the web.config that is different from the version of the deployed assembly (2013.1.417 I assume). The Upgrade Wizard should take care of the correct update of the web.config. However it might have happened something unexpected. To solve the issue, you should update the reference in the web.config to match the version of the deployed assembly. You could also check if the Telerik references in your project are the version you have upgraded your porject to.
Another possible reason for the issue could be older version of Telerik.Web.UI
in C:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files
directory. Delete the content
of this folder and try again to run your application.
If none of the suggested works for you it would be great if you could send us a sample project reproducing the issue, so we could examine it.
I am looking forward to your reply.
the Telerik team
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