Mercedes C220 Immobliser problem?

Moved my C220 off the drive the other day, returned half an hour later to drive off, & the immobiliser won't turn off, therefore car won't start. The green light on the interior mirror flashes constantly when ignition is on, red light on the mirror doesn't show anytime, & the red light on the door handle doesn't show any more when the car is locked & alarmed. The AA say it's a Mercedes dealer only job, local auto electrician has suggested various battery disconnecting solutions, none of which have worked. It's going to Mercedes on Monday, but I'm hoping there might be a reset procedure somebody can help me with.
Any info appreciated, thanks in anticipation.