I seem to have been reverted to just being a "subscriber" to the forum when I was a "sponsor" before, and presumably actually still am!
Also my forum settings are set to automatically "follow" any threads that I post in, but I wasn't getting any e-mails about new posts in this thread, and I've now had to subscribe to it manually, so it looks as if that facility isn't working now either!
How strange that the new forum software, although it took a bit of getting used to, did work reasonably well for ages, but now seems to be all going wrong!