X5 central locking wierd problem

[joynt2002]

Hello all , i have a 2001 X5 3.0d . When i buyed the car the central locking worked perfect, but from 1 week i can-t lock the car from the button on the key, just locking from the door lock...i went with the key to a local key shop and they have tested if the key is transmitting when i press the lock button.The tester shows that the key is transmitting something. I have also changed the door locking mechanism with actuator and everything and still doesn t work. The locking button inside the car works, what can it be ?
Do you think i have to reprogram the key , or where to start searching ? Thank you