Awww, THANX for the sympathy, George. Your suggestion probably wouldn't work because it's still the same page it was before and, from Chris' answer, there is probably something wrong with the data in the page but the error message is not providing any information about the problem.
It's too late for any help now - as soon as I saw Chris' answer, I did it on a fresh page. This time, though, I tried something different on the chance that it was data I had entered that wasn't being accepted. I had the sources in another window and didn't remember the death date when I tried the first time, but I did enter the death place then. I suspect that caused the system to cough and sputter. Anyhow, the second time I did it without entering the death place and it worked fine.
I really, really appreciate your kind thoughts, though.