How do you join a forum?
Forum or group? For replying to a forum thread, just make sure you are logged in. For groups, you need to join before posting. The join button is on the left side of the screen. For open groups the join is immediate. For closed groups, you must be approved by a moderator, so you can get the not joined message even after you think you are already a member.
That's what I would have expected, but trying to reply to a Forum topic gives me Sorry, you are not a member of this group and I assure you I was logged on.Also I can't find a list of All Forums, or a search by Forum name.
You are replying to a Forum topic with the above post.
I have solved it. Firstly the message in people's updates when they post to a group discussion uses the word Forum, and is then displayed just like a forum. That's why I got into my predicament. Secondly, when looking for a Group, using Search, I didn't find it because the name of the group is Naked at home - 2014 / 2015 and the name of the Forum is Naked at the home. Just call me Sherlock in future!
Thanks for all who helped.