Focus Mk1 Central locking

[jmn]

This has recently failed to operate from the Key Fob.
Key Fob battery is good.
Car centrally locks OK from driver or passenger door.
Hatch will not unlock from Key Fob but OK from dash button.
Any suggestions as to what is the likely problem?

[Zetec-S]

Does the key fob need to be "re-synced" with the car...?