I have just finished developing a game, and I sent out testing versions. I have one user whose computer can run games like F.E.A.R. and Bioshock exceptionally, and my game is nowhere near that good. However, when he attempts to load a level, it crashes. It loads the level, and then sets up the pathifinding. Then, at the last second, it sets up the graphics and starts up the player's action. My tester can see a fraction of the level, and then it crashes. I have set up an installer, so everyone got the same game. I also sent out several other versions, and everyone else had no problems.

What could cause a game to crash on just one computer? If the final(published) version is issuing no errors at the beginning, what could cause it to fail later?