citroen berlingo immobiliser?

I have a 2006 Berlingo Multispace. The headlamps and all dash warning lights come on in the middle of the night while the car is locked up. This mainly seems to happen when there is a frost (or snow). The remote locking doesn't work but by unlocking the door with the key that turns off the headlamps and all warning lights. I now have to disconnect the battery every night so that it doesn't go flat.
Not exactly the same fault as the first question but the 2 faults must be linked in some way.
Anybody got any ideas? My local Citroen main dealer hasn't got a clue!

David
January 2010