Hi there,

I reckon you could handle endRequest event of the PageRequestManager class:

<script type="text/javascript">

    function onEndRequest(sender, e)
    {
        var err = e.get_error();
   
        if (err != null &&
            err.name === 'Sys.WebForms.PageRequestManagerTimeoutException')
        {
            e.set_errorHandled(true);
        }
    }

    Sys.WebForms.PageRequestManager.instance.add_endRequest(onEndRequest);

</script>

hope this helps