$(document).ready(function() {
    Sys.WebForms.PageRequestManager.getInstance().add_beginRequest(BeginRequestHandlerExport);
    Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequestHandlerExport);
});

function BeginRequestHandlerExport(sender, args) {
    BlockUIDivCenter();
}

function EndRequestHandlerExport(sender, args) {
    UnBlockUIDivCenter();
}