I had this happen 2 weeks ago in freezing weather and had to get my kid into the back seat Dukes of Hazard style through the window!
I changed the 15 amp fuse (#54 or 57 as I recall) and that didn't seem to work - fuse blew first time I tried using the locks.
Take the car in for service because it's still under warranty and their fix? They upped the 15 amp fuse to a 25 amp fuse and "tested" the system. Unbelievable that they would charge people for this if not on warranty in my opinion but it was the final straw and my car is BMW's again in 8 days.
New one is on the way complete with warranty and hopefully no electrical gremlins (door looks wasn't my first electrical issue).