I finally got another game with the ATCSHD map, so I can give a more detailed description of the problem. It was on a new version of the map, but the same error occurred as before. The error happened the very first time I exited the human base. As I ran around the right side of the wall in front of the lower base exit, it happened, in the exact same place as previous occasions. With no warning, the game suddenly freezes. Nothing is moving; the console cannot be used. Also, the same bit of sound loops continuously. Windows 7 says, "The ATI display driver stopped responding, but then it recovered", or something like that. The game of tremulous, on the other hand, does not recover. The screen is all washed out, and I have to go "Reactivate ATI color controls." Then, I must delete the process of tremulous-gpp.exe *32, that is, if I do not wish to hear the turrets or whichever structure beeping all day.