Suggested fix (unconfirmed): Load your last save to get out of the prison.
The problem
I fell down to from Inner Hall to Level 3 Prisons, rested in a bed and spawned a guard right in front of the only door out. After killing the guard I can't seem to be able to interact with the door to leave the prison, only the guard corpse.
So! I was having the same problem, after a quick google search I found this discussion in a rpg maker forum: "1- Go to your app data folder in Windows (C:\Users\[Your Username]\AppData\Local).
Suggested fix (unconfirmed): Press F5 to reload the game when the error appears. Alternatively, use the defend action on the second turn to avoid dying during the Elite Guard's special attack.
Suggested fix (unconfirmed): Open the `rpg_core.js` file using Notepad. If you encounter an error trying to open it, ensure you are selecting the correct file located in the game's `www\js\` directory within your Steam installation folder.
Day One Fixes