The locks have stopped working on my 2001 Ford Transit?

Ford Transit fwd 2.0L 2001 -280 model.
The door locks on the cab of my Transit started playing up a while ago. On occasions they wouldn't lock with the key fob. I changed the batteries in fob, still no better.
The side & rear door lock/unlocks ok with key fob.
Now neither front cab doors will lock/unlock with fob.
The passenger door locks/unlocks with key, but the drivers doesn't. Any ideas?
Is this a common fault?