how to disable a jqgrid select list (dropdown) on the edit form

This is strange and any alternative method to what I want to accomplis开发者_如何学Pythonh is welcome. My app uses the jqgrid 3.5.3 and I need to disable a select list on my edit form. When I do so using the code displayed below it breaks the edit form - meaning I can not cancel or submit it. Thanks. This code is in the edit options array of the navGrid method. The the dropdown is the 'serv_descr' field. The others are text boxes and don't pose a problem. The form does come up and the field is disabled - its just broken.

beforeShowForm: function(eparams) {

         document.getElementById('equip_id').disabled = true;
         document.getElementById('service_dt').disabled = true;
         document.getElementById('serv_descr').disabled = true;
         document.getElementById('calc_next_svc').checked = 'true';
     }

afterShowForm: function(eparams) {

  $('#equip_id').attr('disabled', 'disabled');
  $('#service_dt').attr('disabled', 'disabled');
  $('#serv_descr').attr('disabled', 'disabled');
  $('#calc_next_svc').attr('checked', true);

}

Note: replace event trigger afterShowForm id name must be form controll