57 plate fiesta studio car doors unlock as soon as I lock them

[Iota117]

Hi all, 

recently I have been having a problem with my Ford Fiesta studio where when I lock my doors (either side or on the inside) they immediately unlock. This is a five door car and I have to lock the doors with the key in the car door as it doesn’t have a fob. Any ideas how to remedy this? I have tried unplugging the inside electrics but I don’t like this option as you loose the horn and the buttons for the boot. 
 

thanks in advance. 

[Paulkp]

Do you have any "Door Open" alarms when all doors are shut and ignition on ?

If the central locking thinks a door is open, then I don't think you can lock the car.