I will come clean and admit that I crashed the server while trying to work on upgrading this system. I had a more recent backup copy of the forum database available but there were problems with restoring the data. In the end, I had to load from a .txt data dump rather than from the PHP .sql export.
There was an apparent denial of service attack on the site last night, with over 200,000 hits on the forum in a one hour period. The good news is that the attack was not successful in itself.
I believe that once PEBKC errors are eliminated, that the system can be trusted to be stable.