When this happened on my Vauxhall a short while ago the locksmith explained that the key had been turned 90 degrees into the deadlock position and because it wasn't a feature that I had used before the mechanism had frozen in that position.I couldn't open other doors either. He emptied half a can of WD40 into the lock and then using his hand hit the car door beside the lock. I was lucky that it freed the lock because it would mean a strip down of the door.
arthur
October 2006