cannot lock my renault laguna with my keyless pad?

I have a 2005 Renault Laguna with a 2 button keypad to operate the car, that is to open and lock doors,to set the alarm and to start and drive the car.Everything operates except I cannot lock the car using the keyless pad, if I lock the car using a key in the door handle I can then drive the car and if I park up and lock the car with the key, when I come back I can open the doors using the push button pad. I have replaced the battery.... no good. help