I solved the problem, kind of. Maybe this is a bug.
The originally posted problem happens--it starts up in "failed update" mode--if and only if I have a tone preset with "No amp" as the model in tone slot 1A. Any amp model other than "No amp," and it starts up normally and plays normal.
I don't know why it should be that I can't have a preset with no amp at 1A, but that appears to be the case. It only took me about a day to test presets to figure out the variable that was causing the problem...
