I've found a bug which makes it impossible to proceed through the game. It seems that when you do things in a particualar sequence, the adbot needed to open the vent ceises to fly around and freezes near the collapse monument. Here's the exact sequence of things I did until I encountered the bug:
The only thing I could do was to restore a previous save and enter the vent with the help of now moving WATICorp Adbot before I entered Pandemonium. Anyone else encountering the same problem?