I have Ati card too and same problem. On windows you can try change 'api' paramter from 'default' to 'pandadx9' in game_options.txt in POTCO game directory. I think OpenGL support of Ati cards to buggy, but on my computer directx woking well. See instructions here :
http://www.piratesonlineforums.com/f...20202#poststop