I believe there are different permissions on each FORUM. Likely on each thread in a forum, too. Some are member only. Some are lifer only. The new grouping is the lowest permission, with posting to only some forums. Over the years these distinctions have become blurred. In the midst of the spam attack there was at least one thread that could be posted to by the spammer, but he could not post to the others.
Please mail any problems to the admins (usually Ryan or Roger.) They will also need your help with the NAME of the forum and the TITLE of the thread. Again, the old restrictions may now be better enforced, so, you might just get a nothing when you click on it. For example: BPL Members Only may still not be assessable. Many of the permissions need to be rebuilt, no doubt.