Z4 central locking

[lovelife]

Hi all, is there anyone who can advise me.

My central locking on my z4, 04, is playing up in fits and starts.
Locking doesnt seem to be a problem once the system unlocks, but sometimes when i go to unlock/unarm the car using the button on the key the buttons dont come up and the doors dont open.
I then have to open the drivers door putting the key in the lock and the alarm will beep then i deactivate it pressing the centre part of the key.
The passenger side at this point does not open. I cannot get the passenger door open from the outside or the inside.
Once in the car when i press the interior locking switch near the gearstick it will lock the drivers door but then not open either drivers or passenger side so i had to open the window and use the key on the drivers side to open the door.

When using the internal locking switch it does sound like its trying there is a noise but its as if theres something sticking on the passenger side.

then all of a sudden the system works fine again.

I first noticed it when we had some frost. its been ok since then it happened again today when we had had some rain. Dont know if that is effecting something.

Can anyone help

thanks
Mike