function OnAjaxRequestStart(sender, args)
{
    if(args.get_eventTargetElement() != null)
    {
        args.get_eventTargetElement().disabled  =   "disabled";
    }
}

function OnAjaxResponseEnd(sender, args)
{
    if(args.get_eventTargetElement() != null)
    {
        args.get_eventTargetElement().disabled = "";
    }
}