G'day folks...

So I have a problem which doesn't seem to be too uncommon, but buggered if I can figure it out. Twice now my housemates 2003 Freelander has decided to apply the immobiliser at seriously inconvenient times. It seems random; once was directly after locking it with the fob, and once was automatic after I left the the car unlocked to try and prevent the issue. I've tried re-linking the key (lock, unlock, lock x 5), and I've tried hitting the central locking reset button near the fuse box, since that apparently sorted it out for him once. Anybody know any other tricks to get her started? Last time it seemed to be a question of leaving it alone for 24 hours, but that's a luxury I don't have right now. Cheers in advance.