Purchased Arma 2: Combined Operations just the other day. Used sixupdater w/o any troubles. The wiki mentioned running both games prior to installation of DayZ for multiple other launchers/installers, which did not appear to be required for the sixupdater - I did so anyway. Works fine, no complications. However, if running Arma 2:OA via Steam, it's suggested you run Steam as Administrator, otherwise compiler issues may appear.