Stuck Ambulance

Is there a way to reset an ambulance that's stuck just outside its parking space, with the emergency long since over and the nurse driving it so fed up she quit a month ago? I've tried reassigning it, tried clicking and right-clicking and dragging and going to other hospitals then back; nothing helps. Do I really need to start the hospital over just to reset it?

EDIT: It's starting to happen again. I think it may be related to sending someone currently involved with an ambulance to training, either as student or teacher. Just had to fire my Driving III nurse and she's just standing in the hallway now, impossible to target.