While playing, I have noticed that the game is affected by memory leaks. As time goes on, the RAM used by the game continues to increase until if effects performance (Windows stating out of memory). Eventually, if the message is ignored, the game will actually start reporting errors loading map files.
The result of the failure to load map files include:
1 - inability to enter a building through an open door. I was able to enter other buildings.
2 - Staring at a loading screen, with your quick inventory still shown. You are still in game, but you cannot see. Sometimes this recovers into the game, other times I have had to quit.