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;
	}
}