Sys.WebForms.PageRequestManager.getInstance().add_beginRequest( startRequest );
            Sys.WebForms.PageRequestManager.getInstance().add_endRequest( endRequest );
            
            function endRequest( sender, e ) {       
                document.getElementById("Update").style.display = "";
            }
            
            function startRequest( sender, e ) {                
                document.getElementById("Update").style.display = "none";
            }