Hello Kadji Okou,
Check whether the code behind of the master page looks as shown below
_DefaultMaster : System.Web.UI.MasterPage
Your Inherits attribute does not match the code behind of the master page. You can use VS to generate a master page and Place the code behind
in a separate file.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items.