With the ignition off, hold down the central locking button (it's on the dash or down by the handbrake, not the one on the remote) for at least 5 seconds.
The doors should lock then unlock and the immobiliser light on the dash should light up.
Release the button.
Press the button on the remote twice. Doors should lock and unlock.
Repeat with spare key.
Start car as normal.
victor, May 2009