Got to the end of the game. I was able to go downstairs, but when I eventually tried to go back upstairs, I got the same error for map 100. Fortunately, there was an exit downstairs, so once I restarted the game, I could continue.
This game was fun and very clever. I could recognize a lot of the inner coding being referenced. My one suggestion would be to look into having the "Chicken sound" skill being callable from the Skills menu, like the heal skill is. Never tried that myself, but having the skill call a common event might work.