On May 28, Ed Lecuyer informed me that the forum was showing an error of some kind, looked like the forum database software had crashed.
I was unable to recover us from that state. I tried installing a new version of the forum, but ran into bigger trouble (namely, a blank slate!).
I had our host restore the website to their full backup from Friday night/Saturday morning midnight. The forum is back in operation, minus any posts from Saturday and Sunday. I do not plan to try to recover them.