Hiya I had the same problem on my Vectra and it is because it needed resycing with the car, How I did this was put the key in the ignition turned it to the position just before starting the car, then pressed the lock button on the fob, this should resync the remote with the car, it did take a few mins before it worked.
If this does not work it could be a lose wire in the fob, as this seems quite common.
Tracie, August 2007
