MoE mysteriously went down last night, and it turned out to be a simple problem:
After several years of use, the MySQL tables needed repair.
I had neglected doing this (even if I do it regularly when I work on desktop databases), problems accumulated behind the scenes, and something eventually broke down giving me a message to upgrade the database…
Database Upgrade Required. Your WordPress database is out-of-date, and must be upgraded before you can continue. The upgrade process may take a while, so please be patient.
And then a long list of error messages when I did…
WordPress database error: [MySQL server has gone away]
The fix is simple and explained here: How To Quickie: Repair MySQL Tables.
(Thank God for friendly and helpful folks at the WP user forum.)