Solved Having problems restricting the right to post within a category

You got it right and it certainly was a strange one but through the problem I had with that content hider plugin I resolved it with Kunena also. It's strange but here's what I did to get it working...

I created a new user group called "Subscribers" under "Registered" users and the subscription component does its job perfectly: If a registered user subscribes it changes their user group to "Subscribers". All good thus far.

What I did not do and for some reason is not a documented process is this:

I had to ALSO create a new view level for this group "Subscribers" and once I did that both the content plugin and Kunena started working exactly as expected.

Strange I know.

The Captcha issue was an easy one to solve and as I'd never even looked at that setting in Kunena it was difficult to find but I know for sure Kunena was producing the message so looked around and changed the value from zero to blank.

I want to thank you for your patience on this. Greatly appreciated.

So ... now we can mark this mystery as solved?

I think we can indeed.

There is one minor glitch and that is that although I have set all the sub categories up the same way that when a registered user enters some of them they do not see a "New Topic" button and in others they do but when they click it they get the error that they cannot post which is OK.

I'll mark this topic as resolved and, even though there's a minor irritation here (and you will just have to take my word for it that we have no such issues on this website) the fact that the NEW TOPIC button appears (but is non-functioning) is a reasonably agreeable outcome.

I've checked the forum here and, where sub-categories are involved, asw long as the sub-categories are each set up in a similar fashion to the parent categories, there is no issue of a NEW TOPIC button appearing in those places where users can view topics but cannot post new topics in them.

A case in point, on this forum. Go to just about any "archive" category and you will find that, although you can read the topics and reply to the topics, you cannot create new topics in those categories.