Jérôme Pott 

Or more likely you are just not signed in!

Thanks for the reply! I was able to accept your answer, but I still cannot accept the one I mentioned.

The only reason I can think of is that a few days after I posted that question, my Trados membership expired and I renewed it two days later. It seems that the forum no longer recognize me as the original author of the question, although the question still appears in the Questions tab in my profile.

Jérôme Pott 

That's odd because I logged in as you to take that screenshot.  So I can do that again, click on the red bar to make sure I'm signed in, and then verify the answer.  Shall I do that?

Ah, I just needed to join the discussion group! (I think my question was moved to a group I hadn't joined.) Thanks for shedding light into this issue 
After joining the group, I was able to interact with the discussion.

Jérôme Pott 

That would be it... and it was my fault!  I moved it there earlier as I thought it would be more likely to get a response in there.  Apologies!

No worries Actually the notification should have been better phrased: for example "you need to first join this group in order to participate". Instead of "you need an active Trados membership to participate".

Jérôme Pott 

Jérôme Pott said:

Actually the notification should have been better phrased

I don't disagree.  We were doing some "accessibility" testing with a blind user a week or so ago and one of the things on our list to change was this message because users don't have patience when listening to a screen reader for every button when the messages are too long.  So they move onto the next.  In this case the "Click to join" part was at the end and our user never even heard that bit!

So we will be changing it to move the "Click to join" part to the start and will adapt the message to incorporate your useful feedback too.

Thanks

Paul.