The easiest way to check is to do a search for Telerik.Web.UI references. In the original sample the Register directive is using a different version:
<%@ Register Assembly="Telerik.Web.UI, Version=2009.2.701.35
, Culture=neutral, PublicKeyToken=121fae78165ba3d4" Namespace="Telerik.Web.UI" TagPrefix="telerik" %>
Make sure all references point to the same version.
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