I suggest to examine the following possible reasons for the problem:
- Make sure that you have installed the AJAX Extensions in case you use Visual Studio 2005 and you have opened an AJAXEnabledWebSite.
- There are separated versions for Telerik.Web.UI for both .NET 2.0 and .NET 3.5 frameworks (bin and bin35 folders from the download). In case you use .NET 3.5, please make sure that you have used the Telerik.Web.UI.dll file from the bin35 directory.
In case this does not help, please provide more information about your VS.NET, the framework version you use, and whether you are able to use the other RadControls on the same page or in other projects.
the Telerik team
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