central locking control unit?

when i use the remote to open the car door`s they all unlock even the boot open ok but when i go to lift the handle up to open the driver`s door it will relock it self this only happen`s on the driver`s door the only way to open the driver`s door is to use the key . i have tryed to spay wd 40 on the lock to see if the lock was sticking that was with no joy . i have had the car three year`s and this is the only thing that as played up on it