window.onload = function() {
        var prm = Sys.WebForms.PageRequestManager.getInstance();
            if (prm) {
                prm.add_endRequest(endRequest);
                prm.add_beginRequest(beginRequest);
                prm.add_initializeRequest(CheckStatus);
            }
        }

        function CheckStatus(sender, args) {
            //var prm = Sys.WebForms.PageRequestManager.getInstance();
            if (sender.get_isInAsyncPostBack()) {
                args.set_cancel(true);
                alert('Please Wait.\nStill processing previous request...');
            }
        }


        function beginRequest(sender, e) {
                var divOpoup = document.getElementById('poploading');
                if (divOpoup)
                    divOpoup.style.display = '';
        }

        function endRequest(sender, e) {
            var divOpoup = document.getElementById('poploading');
            if (divOpoup)
                divOpoup.style.display = 'none';
        }