Please help System.Security.Principal.IIdentity' error!

Question

CS1061: 'System.Security.Principal.IIdentity' does not contain a definition for 'GetUserName' and no extension method 'GetUserName' accepting a first argument of type 'System.Security.Principal.IIdentity' could be found (are you missing a using directive or an assembly reference?)

getting this error in Site.master designer file..

 

<li><a runat="server" href="~/Account/Manage" title="Manage your account">Hello, <%: Context.User.Identity.GetUserName() %> !</a></li> 

 

 

GetUserName() havig error 

 Microsoft.AspNet.Identity alredy added

 

thank you!