Here is the missing resource name: pTelerik.Web.UI.Skins|Telerik.Web.UI.Skins.Web20.Common.radGradientListSprite.png You can see if this is your case as well by decrypting the WebResource request that fails as shown here: http://blogs.telerik.com/aspnet-ajax/posts/07-03-27/debugging-asp-net-2-0-web-resources-decrypting-the-url-and-getting-the-resource-name.aspx
Thanks Marin. That is definitely the missing one for me. I can see it in the server application logs.