I replaced the batteries on my key which operates the central locking and the alarm. Now the lock and alarm do not operate with this key. When I insert the key into the ignition, it does not work either. How can I get the car to recognise this key again. I am having to use the spare at the moment. It is W210. Key works the alarm and remote boot opening. It is not the first time that I have replaced the batteries, but I have not had this problem before. Any ideas?