why does my keb fob only open my driver door on ford focus 1.6 ,1999?

on my ford focus 1.6 zetec year 1999 , when i use the remote key fob to unlock the car only the driver's door will open. the rear doors and the passenger door will not open. i have to physically go inside the car to the passenger side and deactivate the inside lock before the other doors will open. does anyone know why this is happening and how i can rectify the problem please so that all the doors will open when i use the key fob?. any help will be greatly appreciated as its driving me mad!!
many thanks
david