Bill,
Bless BlueHost (the hosting company that looks after the website for us...)
I suspect in this particular case it was my fault. My development copy of the databases that form a large part of the website (don't ask, it's scary...) was corrupted, so I needed to grab a clean copy of the current backup. Unfortunately, doing so places a large strain on the server's CPU and could well have caused that error message to appear.
