For several hours today, the discussion forum was not working properly. I traced the problem down to a php/MySQL problem which I reported to my web hosting provider. Although they claim that they did nothing to fix the problem, everything appears to be working again.
This has happened several times in the past. If it happens again, I'm going to ask that they move the website to a new (different) server. If that doesn't work, I'll have to consider moving to a different hosting provider.