I have just answered your support ticket on the same matter and I am pasting the troubleshooting steps I have suggested in this thread as well, in case somebody else stumbles on a similar issue:
This is a strange error and I have not seen it before. Can you confirm that there isn't code that is using the RadControls too early in the page lifecycle (i.e. before the Sys.Application.Load
event)? This is easiest tested by disabling your custom scripts and if the issue is gone you can start re-adding them piece by piece to find the offending one. You can also examine the stack trace of the error to see where it originates from (i.e. where is the call that causes the issue).
It is possible that some of the scripts the controls need to operate properly are not loaded, so I can suggest you take a look at the following articles and see if the suggestions there help:
You can also try the script CDN we offer: http://www.telerik.com/help/aspnet-ajax/scriptmanager-cdn-support.html
so that the scripts are not loaded from your own server, in case the problem stems from the webresource requests.
I can also suggest the approach from this blog post so that you can get the resource that is causing the problem: http://blogs.telerik.com/blogs/07-03-27/debugging-asp-net-2-0-web-resources-decrypting-the-url-and-getting-the-resource-name.aspx
If you are using RadScriptManager you can also try disabling the script combining by setting the EnableScriptCombine property to false.
All the best,
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