Thanks for contacting us.
So we can better assist you, on what page of the CMS do you receive this error? Is it on the pages tab? The modules tab? Is this error happening when you access a custom module? Are you able to log into the CMS or is this error happening when you go to http://www.mysite.com/sitefinity/login.aspx? If you set the application to run in full trust, does this error persist?
the Telerik team
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