Unusual problem with Ford Focus front door locks?

Anyone any ideas of this problem?
Ford Focus Diesel 2002 51 reg estate.
Driver and passenger door not unlocking.
symptoms are:
Put key in and turn to lock and hear the locking noise, all doors lock, put key in either front doors and turn to unlock, hear unlocking noise and front doors dont unlock but back ones do.
I have tried changing the fuse (fuse 63) and its still the same.
I have also tried WD40 in locks plus have taken the side panel off and oiled the metal bits (nothing helps)
Could both front door locks fail at the same time?
I have, If i have to change the locks do i have to change them all and does the central locking unit have to be changed at the sametime?
Im in the UK don't know whether this makes a difference to models?

les
April 2010