Falling through the floor

[Romulator]

This sounds like a missing assets issue. This section of the forum is more related to Amnesia: The Dark Descent, not CS troubleshooting, but given the problems, I believe that you are missing assets, either with Amnesia or A Late Night Drink itself.

Where did you get the game from?

Where did you download A Late Night Drink? Are you certain you downloaded all contents? Do you have Amnesia's 1.2 (sometimes called 'Justine') patch?

Have you experienced any similar problems in Amnesia: The Dark Descent?

Could you run the Custom Story again, and when the problem occurs, exit the game, then navigate to the hpl.log file and post it here? The appropriate directory can be found looking at the Troubleshooting Guide at Problem X.