I tried getting it to work using User Group Promotions but I must have messed somewhere because it failed to work. I created a rule where a member meeting defined criteria became part of a new user group named Regulars. The forum was allowed to be accessed by Regulars and not Registered.
This somehow failed to work for me as the users who were promoted became part of both Registered and Regulars and somehow they followed permissions of Registered so no access to the forum. I ended up deleting the custom user group and the promotion and right now the forum is accessible by logged in members and not guests.
Can someone suggest how to do it the proper way. And if my way is the way to do it, how do I get it right? Thanks.