How can I fix my central locking remote control on Renault Laguna?

My Renault Laguna (1998) ignition key has remote control for the central locking - squeeze the key, a little red LED lights up and bing the doors unlock - usually. Anyway - batteries died, so I replaced them (with the correct one), LED lights up fine again now but the car doesn't seem to recognise the signal (doesn't respond at all...). Can still open door by putting key in lock but ideas on what might be wrong with the remote would be helpful.