Mehehee... I see someone got a problem here. Old topic but anyway I'll reply.
I play Fot Co-operative on GameSpy since 2 years, and i am walking knowledge about oos problem. It's weird. Oos was made to disable hexxing and cheating. Sometimes you got it in Co-op games, It's a popular problem. But hight instalation and well installed maps may remove the problem, different thing is that you need to test all new maps that Darsiders (co-opers ]:->) make.
Coop community is still alive, you need GameSpy and open ports to play it.
Rooms are usually at 18-24GTM, not every day.
Don't try to play by IP, becouse then you got 100% oos chance - tested alot of times, some people can't play by that ;/.
Big library of maps and Co-op info here:
http://www.fot-community.tk
http://www.republika.pl/koneo/
I'm not playing Fot now, but community is still active... Not many people there, but theres always chance to find room.