It could be that the remote needs resynchronising with the car (also called programming).
30 seconds with Google found this:
http://www.lifestylefordparts.co.uk/article/show/13
https://www.youtube.com/watch?v=mG3R58-24QU - Sickeningly simple!
https://fordtransit.org/forum/viewtopic.php?f=54&t=67293
XX, September 2015