Hello Francis Rosos,
Please make sure you have successfully deployed ASP.NET in your SharePoint site. RadTabStrip for ASP.NET Ajax requires the same. You can find detailed instructions in this web page
http://sharepoint.microsoft.com/blogs/mike/Lists/Posts/Post.aspx?ID=3
Using RadTabStrip for ASP.NET Ajax also requires the Telerik.Web.UI.dll assembly to be installed in GAC. You also need a SafeControls entry in your web.config file:
<SafeControl Assembly="Telerik.Web.UI, Version=2008.1.415.20, Culture=neutral, PublicKeyToken=121fae78165ba3d4" Namespace="Telerik.Web.UI" TypeName="*" Safe="True" />
You an also try enabling the stacktrace of your SharePoint web site - this would show more detailed error info about the error. To do so set the
CallStack attribute (of the SafeMode tag in your web.config) to
true.
<SafeMode MaxControls="200"
CallStack="true"
Regards,
Albert
the Telerik team