My Ford Focus central locking doesn't work correctly?

I've got a 2002 Ford Focus LX (Diesel) and the drivers door lock doesn't operate from the remote. If I try and lock using the remote the locking locks/unlocks, I can manually lock the drivers door with the key, which locks all doors, I can then unlock all other doors using the remote but have to manually unlock the drivers door.

I've seen this question a few times but haven't seen any answers, is it fixable myself?

Thanks.