There's also a speed limitation, though I can't recall offhand what it is. My car shows the Autopark icon relatively frequently, but I have yet to use it.A couple of things come to mind:
1) How many miles do you have on the car? It won't enable AutoPark until you have at least several hundred miles -- needs to calibrate.
2) How close are you to the cars? You need to be closer than you would otherwise be so the sensors can "read" the cars and the gap.
3) You must have a car - gap - car for the AutoPark to detect a spot.