Disabling UPS for certain categories

[getyler2]

I need to disable UPSXML for categories 1, 38 and 39. I've read several threads on this and think this is all I need to do, but it doesn't work. Probably a syntax thing. Ideas?

Add this code to /includes/modules/shipping/upsxml.php. The commented out code is another unsuccessful try.

            if ($check_flag == false) {
                $this->enabled = false;
            }
// disable if master_categories_id 1 is in the cart
//      if ($_SESSION['cart']->in_cart_check('master_categories_id','1') > 0) {
//          $this->enabled = false;
//      }
// skip certain categories
      if (IS_ADMIN_FLAG == false && $_SESSION['cart']->in_cart_check('master_categories_id','1') > 0) {
        $this->enabled = false;
      }  
      if (IS_ADMIN_FLAG == false && $_SESSION['cart']->in_cart_check('master_categories_id','38') > 0) {
        $this->enabled = false;
      }  
      if (IS_ADMIN_FLAG == false && $_SESSION['cart']->in_cart_check('master_categories_id','39') > 0) {
        $this->enabled = false;
      }  
          }