I have public variable 'MessagePlaceholder' on MasterPage and a Class that accesses this property like that setting it's value to string from getMessage();

((HttpContext.Current.Handler as System.Web.UI.Page).Master as MasterPage).MessagePlaceholder = getMessage();

which gives me an error like this one

Error 3 'System.Web.UI.MasterPage' does not contain a definition for 'MessagePlaceholder' and no extension method 'MessagePlaceholder' accepting a first argument of type 'System.Web.UI.MasterPage' could be found (are you missing a using directive or an assembly reference?)

What should i do ?