function showtbloading() {

             var target = $("#GridView1");

             if (target.length <= 0) {

                 $("#tbloading").width($(window).width());

                 $("#tbloading").height($(window).height());

             } else {

                 $("#tbloading").width(target.width());

                 $("#tbloading").height(target.height());

                 $("#tbloading").css("left", target.offset().left + "px");

                 $("#tbloading").css("top", target.offset().top + "px");

             }

             $("#tbloading").find("div").eq(0).css("top", ($("#tbloading").height() - 32) / 2);

             $("#tbloading").show();

         }

         function hidetbloading() {

             $("#tbloading").hide();

         }

        <div id="tbloading" style="position: absolute; top: 0px; left: 0px; filter: Alpha(opacity=50);

            -moz-opacity: 0.5; opacity: 0.5; background: #777; background-color: White; z-index: 1000;

            display: none;">

            <div style='width: 32px; height: 32px; left: 50%; position: relative; text-align: center;'>

                <center>

                    <img src='/pic/Rotate.gif' alt="" /><br />

                    <span style='font-size: 13px; font-weight: bolder; width: 100%; text-align: center;'>

                    </span>

                </center>

            </div>

        </div>

         Sys.WebForms.PageRequestManager.getInstance().add_beginRequest(PageLoadingHandler);

         function PageLoadingHandler(sender, args) {

             showtbloading();

         }

         Sys.WebForms.PageRequestManager.getInstance().add_pageLoaded(EndRequest);

         function EndRequest(sender, args) {

             hidetbloading();

         }