So now and then when I'm loading a map it instead kicks me back to the normal Q2 main menu. When I exit and return to game I've lost my inventory as though I'd died. I'm running windows 7 x64, with non-steam Q2 with EGL. I tried Q2XP as well, which both did this and crashed to desktop when I went underwater. Does this happen to anyone else?

Crashing while in water sometimes hapens with the regular Q2 engine (when you use software instead of openGL). Try using the classic Q2 engine (on openGL , of course) and check if it crashes on it too. If it doesn't it might be because of EGL / Q2XP

Unfortunately I cannot run Q2 vanilla on anything other than software. Default openGL crashes to desktop and any other option just kicks it back to software. I can try running software for a while to see if it happens again, but I'd REALLY rather not play it that way.

Does Evolved work with CoopOrDie?

EDIT: Just tried Quake2maX got a "Buffer Overrun" fatal error consistantly. No idea what that is...

EDITALSOEDITEDIT: Software seemed to work fine. However it still crashes underwater. >.<

MoreEditToAvoidManyPosting: So I think it may only boot me back to menu if I push a button while a level is unloading (before the "loading" screen appears but after the screen goes black at the end of a level). Not 100% sure yet but I've been playing for a bit on EGL with no problems being very careful to not push any keys during this time.

Do you have an ATI video card?

Also, try this thing: http://www.coopordie.com/forum/viewtopic.php?f=7&t=493 . It might repair your openGL problem.