Originally Posted by BigWalleye

My experience has been that ALT-TABing brings on the CO2 problem, sometimes with as little as one ALT-TAB. The mission in progress can be recovered by saving the game, exiting the program, and restarting. When the mission resumes, the CO2 bug is gone. But I believe there is a simple way to avoid this problem: Don't ALT-TAB from an active game. Pause the game by going to the Options menu. Then ALT-TAB out. I haven't noticed any problems when I use that routine. Has anyone else had a different experience?