[support] How can I get the error message from database

For some reason one of my queries is not executing. I've used the db_error() but I only get 0. I'd like to know how can I get the error message. I am using drupal 6, MySQL. $success = db_query("INSERT INTO {user_profile_fields} (uid, username, id_center, telephone, street, city, distt, country, zip) VALUES ('$uid', '$username', '$idcenter', '$telephone', '$street', '$city', '$district', '$country', '$zip')"); if(!$success) { // here I am using the $error = db_error(); } Regards.