Sys.WebForms.PageRequestManager.getInstance().add_endRequest(function(sender, args) {
    if (args.get_error() != null) {
        if (args.get_error().name === 'Sys.WebForms.PageRequestManagerParserErrorException') {
            // remember to set errorHandled = true to keep from getting a popup from the AJAX library itself 
            args.set_errorHandled(true);
            window.location.href = '/frmSessionTimeout.aspx';
        }
        if (args.get_error().name === 'Sys.WebForms.PageRequestManagerTimeoutException') {
            // remember to set errorHandled = true to keep from getting a popup from the AJAX library itself 
            args.set_errorHandled(true);
            window.location.href = '/frmSessionTimeout.aspx';
        }
        if (args.get_error().name === 'Sys.WebForms.PageRequestManagerServerErrorException') {
            // remember to set errorHandled = true to keep from getting a popup from the AJAX library itself 
            args.set_errorHandled(true);
            window.location.href = '/frmSessionTimeout.aspx';
        }
    }
}
);