var prm = Sys.WebForms.PageRequestManager.getInstance();
prm.add_initializeRequest(initializeRequest);
prm.add_endRequest(endRequest);
var postbackElement;

function initializeRequest(sender, args) {
    document.body.style.cursor = "wait";
    if (prm.get_isInAsyncPostBack())
    {
        args.set_cancel(true);
    }
}

function endRequest(sender, args) {
    document.body.style.cursor = "default";
}