FYI -- I have done all these things -- repeatedly -- and they did not resolve the issue.  However, the most recent revelation from data services is that this has actually happened before to another customer and that it was the result of a corrupt Windows or Windows user.  So I created a new Windows user and have been running QB on that now for 3-4 days and have not seen the error since.  I was not able to go that long without an error before, so I believe that this might indeed be resolved.  I will post back in another week if I have no further encryption errors pop up and post the solution as a corrupt Windows user.