try spraying some WD40 into the latch mechanism, and operating the door handle a few times. that may free it up...
This would happen to my Passats in German winters all of the time. It's something to do with the latch of the lock on the side of the door not talking with the door handle.
Lube where the key goes + the internals mechs in the actual lock area where the door latch is. It will eventually loosen up and work properly.
I use spray cooking oil like Pam or a generic brand. Works better as a lube than WD-40 without all the nasty chemicals. It's my secret weapon for squeaky doors, any gears, and stuck metal fittings. Easy to find in the house and never gets lost. :thumbsup:
In fact, I saved my mom from a plumber's visit last week after a pipe broke under her bathroom sink and everything was frozen with rust. She's allergic to WD-40, so that was out of the question. Within 1 minute, everything was free turning to shut off that sink's water line instead of the entire rest of the house.
good luck & hth :thumbsup: