So, I've set up a Privare Forum, gave Mod status to some users, changed the Forum permissions to only allow them acess and...

they cannot access it.

What have I done wrong?

They also need to be assigned as a moderator of that forum. Basically, in 7.3+ this allows moderators to have varying rights in each forum. So, you can either pull up the moderator directly and add him as a moderator of said forum, or you can bring up the Moderator Permissions screen and add them to the forum there.

Right,