The error denotes that the runtime cannot find the RadControls assembly. This could happen if the Telerik.Web.UI
assembly used by the website has been deleted from the website BIN, or removed from the GAC.
Are you creating a WebSite or a WebApplication?
Can you send us the web.config file?
Can you check if you have the Telerik.Web.UI assembly in the local BIN folder of the project?
the Telerik team
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