Hi! I know whats the problem
I must have one of the 4 doors jammed havent you?
probably one door doesnt open when you want to open. When you press to open the central locks open all the doors, but one door mechanismc stays close because its jammed. Then the central locking system locks again!
When you can open your door look at the other doors and see if they are all open. If you is jammed you can fix it, need a bit of engineeering!
- dissasembly the door trim and remove the door locking mechanism.
Then with a nife you can "break it" and open (i think its sealed).
Then you must remove the small electric motor, and your problem must be the brush of the electric motor dirty! Clean the colector (the area of contact of the brushes)
- Put togheter with glue and thats it!
Or buy one used on ebay!
(Im portuguese so Im sorry for my English I didnt have time to translate)