central locking fault on citreon picasso?

i have an intermittent fault with the central locking on my '55 citreon picasso. i press the key fob to unlock the car and it will unlock all the doors apart from the drivers door, i have to lock the doors and try again and on the second or third time of trying it will open.the next time i go to unlock the doors it will open first time! any ideas

carl66
February 2009