try {
    Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequestHandler);
    function EndRequestHandler(sender, args) {
        if (args.get_error() != undefined) {
            if ((args.get_response().get_statusCode() == '12007') || (args.get_response().get_statusCode() == '12029')) {
                //Show a Message like 'Please make sure you are connected to internet';
                args.set_errorHandled(true);
            }
        }
    } 
} catch (e) { }