Index files
The problem has something to do with Windows discarding a possibly corrupted index file after a crash. It's not a big enough problem for me to do something serious about it--the backup utility for my browser/e-mail takes about fifteen minutes to run and I don't do it every day.
But if someone directs a post at me somewhere in this sea of blue, and I miss it, that's why. Robert's "new post" utility is very helpful.