There seem to be a number of threads complaining of the same problem with ChatterBox: installs fine, creates list but does not add messages to the list. So rather than try and reply to every thread with my solution I am starting a new thread here for all
I have no idea why this fixed it, but what worked for me was this:
Manually add an entry to the list from the list view page. Once I did that, the ChatterBox control worked fine and appended messages to the list.
I hope this helps anyone having similar problems.