//  register for our events
Sys.WebForms.PageRequestManager.getInstance().add_beginRequest(beginRequest);
Sys.WebForms.PageRequestManager.getInstance().add_endRequest(endRequest);    
 
            
function beginRequest(sender, args){
	// show the popup
	$find(ModalProgress).show();        
}

function endRequest(sender, args) {
	//  hide the popup
	$find(ModalProgress).hide();
}