var prm = Sys.WebForms.PageRequestManager.getInstance();
prm.add_initializeRequest(InitializeRequest);
prm.add_endRequest(EndRequest);

var btn;
function InitializeRequest(sender, args) 
{
 document.body.style.cursor = "wait";                
 var btnId=args._postBackElement.id;
 btn= document.getElementById(btnId);
 btn.disabled=true;
 btn.style.cursor = "wait";
}

function EndRequest(sender, args) 
{                
 document.body.style.cursor = "default";    
 if(btn!=null) 
 {
     btn.style.cursor = "default";
     btn.disabled=false; 
 }
 
}