I didnt try the campaign yet, but i have the problem everywhere else...I will delete my profile.cfg, to have a completely clean Arma 2 Combined ops, and I hope it will help.
VIPER, sorry, I just read the titles
Added 10 minutes later:
deleting the savegames didnt solve the problem, so I downloaded the latest beta patch, build 71900, and now i can load games...yet :)