ToME: the Tales of Maj'Eyal

When you are the Gloom dungeon (the one near where elf characters start the game), if you are in a cloud of blackstuff (I'm not sure what it is always) on a stairwell, and then you go up the stairs and back down the stairs again, that is, you land into gloomy stuff on a level, a lua script error always appears.

Sorry I can't describe this better!