fiesta st 150 2007 6000 CD FBB 300,,as the title suggests after reconnecting the battery the unit will not accept its code i just says incorrect now 6 times !, i know its the correct code as i have used it before with no problem and i have the ford radio card with the matching serial number as a double check , the battery was only disconnected for a gearbox change .and all other electrical systems are working fine it powers up fine and both its power feeds are good , i guess it might just be a faulty unit , any thoughts ?