Cancel my problem. I know what happened. I was impatient. The immunization was taking very long, much longer than usual, and it looked like it had frozen up -- I couldn't even minimize S&D. I let it run for a long time this evening, and everything is OK.
However, suggest you consider adding some feature that lets the user know that "something is happening" so that the wait doesn't appear to be a freeze.
Thanks for a great product!