Thats cause the CBA addon linked there is actually an older version. With ACE1.5 they released an updated version. Thats what we are hosting, additionally in the OA download section there is also
a CBA addon. That one you need if you run OA only. But it requires the CBA addon for Arma 2 as well.
I informed the ACE team about these issues but was told I was making it unnecassary difficult and people only needed one version. But that version is not linked correctly. So, yep, its a mess. Dont blame me