1998 129 door locking problem

[Southcoaster]

I have a 1998 129 ....I recently misplaced the key I have been using for the last two years,fortunately I have a spare key, but the problem is that although the spare key remotely locks and unlocks the car and both door buttons go up and down,I cannot open the drivers door from the outside,I can pull the handle when the door button is up and it still won't open! I am now having to enter the car via the passenger door and opening the drivers door from inside.This problem has only occurred since using the spare key,any ideas for a remedy gratefully received .