Thank you Vessy for the reply,
I did try adding this in our webconfig but still not working.
For the <telerik:RadScriptManager runat="server" EnableCdn="true"></telerik:RadScriptManager>
the EnableCdn="true" is not existing methods inside the telerik control
Any other advise, I feel the issue is in the machine key.
Do you know how i can overwrite using web.config with telerik as this server is also shared with other sites?