i have had same fault,here is my solution.
you will need to take the battery neg earth connection off and then after about 10 seconds put back on,this will allow you to then use the key blip to reset ,aim it at your mirror and blip once to lock the door then again to open the door you then can start the engine and hopefully you are back where you where before the fault appeared,you will need to reset clock,radio etc but cheaper than a visit to the garage.apparently this is a common fault on this age of w210 merc hope this helps bob.
bob gibney, January 2008
