1. Open the app/functions/fn.catalog.php file in the root directory of your CS-Cart installation.
  2. Find this line:
    if (!empty($params['force_get_by_ids']) && empty($params['pid']) && empty($params['product_id'])) { 

    and replace it with:

        if (!empty($params['force_get_by_ids'])  
            && empty($params['pid'])  
            && empty($params['product_id'])  
            && empty($params['get_conditions'])  
        ) {