The area which I'm talking about is in Turnip Hill, right after the drawbridge. The small elevator in question is locked with a purple keycard.
There's nothing wrong with unlocking it the FIRST time, but if you ride it down, leave the door down there open, go up to the roof of the convenience store, and jump down from it, and then walk all the way up to the drawbridge and the elevator, then you can't call the elevator again. You can push the button, and you'll HEAR the elevator arriving, but behind the door the elevator is probably stuck down there because of the open door, and the door up where YOU are at, won't open again. This makes you permanently stuck.
I'm so glad that I have backup saves.