[kNeo]

Just an FYI but some guests, if not all, are mostly just googlebot or bing or other search indexers. Even if they're on a thread, all they're seeing is "permission denied" or whatever.

As for the permissions just make sure you've set the proper permissions for the default usergroup that most people have as "primary"; and then for the secondary usergroups that allow access to the subforums -- make sure you update them whenever you make new subforums (new forums created default to open for old usergroups, if I remember right).

So, eg:

You already have private forum A, a primary usergroup of 1, and a secondary usergroup of 2 that allows access to A; but you make Private Forum B, but don't change the permissions for usergroups 1 or 2, so they default to getting access to it.

At least I think that's how it goes, it's been awhile since I've made private forums like that. Not sure if that will help.. Now if you want some real fun with permissions, check out phpbb's; ugh.