pretty much what it says in the title. monoliths and vending machines can spawn too close to one another and block pathways. Here's a screenshot of what i mean:
Your friends in this situation are probably concussion bombs, the psychokinetic shove skill, and other such "push" methods. Most such objects can be moved. If your progress is blocked, there will be other exits on the level, even if you have to go up a level first and down another exit to get around the obstruction (or, since that's the level 1 tile set, down then up again if your tastes run to clearing entire floors).
