Sticklebrick

I have a similar problem, the key physically starts the car via the ignition but will not lock the car when trying to use the buttons on the key's fob. I've changed the batteries and it appears to be working because the LED lights up on the fob when the buttons are pressed. The central locking can be operated from inside the car. The stereo is also not the the original, I fitted the stereo myself using an amp bypass lead. The fault with the key/central locking didn't arise until sometime after the stereo exchange. Any Ideas?

Please help! I have a Lexus IS200 1998 Model. I have a fault with the either the Master Key or the Central Locking not sure which. The key is able to open the boot, the drivers side door by inserting it into either of the locks, and it also starts the engine via the ignition. But the key will not unlock or lock the car using the buttons on the key's fob. I've tried changing the batteries. The key fob appears to be working as the LED lights up when the buttons are operated. The central locking can be activated using the buttons on the drivers side door. Can anyone advise as to what might the problem? Thanks