Hi. Thanks for quick reply.
I am still getting the error when try to enable the module. This is what I have:

my_module.info :

; $Id$
name = My Module
description = My customizations to Ubercart
package = Custom

my_module.module :

<?php
// $Id$

/**
* @file
* Module to hold my customizations to Ubercart
*/

/**
* Implementation of hook_form_alter()
*/
function my_module_form_alter(&$form, $form_state, $form_id) {
if ($form_id == 'product_node_form') {
$form['base']['model']['#type'] = 'hidden';
}
}

Both files are place in sites/all/modules/custom/
Can you see what wrong with the codes? I am running D6.9, Ubercart-6.x.2.0-beta3

Thanks.