disable line item fields

I'm having some trouble disabling line item fields in a custom sales order form.

here is the code I'm using.  This code get's called in my OnFieldChange depending on what item was added.

//  ---------------------------------------------------------------------------  //  //  DisableLineItemFields(defaultQty)  //  //  To minimize errors, disable fields that shouldn't be edited by the user and  //  set the quantity to the value of defaultQty.  //  //  ---------------------------------------------------------------------------  function DisableLineItemFields(defaultQty)  {   //  set the qty   nlapiSetCurrentLineItemValue('item', 'quantity', defaultQty, false);      var fields = new Array('quantity', 'units', 'description', 'options', 'rate', 'amount');   for(var i = 0; i < fields.length; i++)   {    nlapiDisableLineItemField('item', fields[i], true);    }  }

'options' and 'rate' aren't working.  I've looked over the docs and don't see any reference for these field names.