Copy of Craft instance generates "An unknown error occurred" for login
So I am going to answer my own question here: The solution was that something, I don't know what, what messed up in the DB. So I dropped the DB and then copied it over again from the original. That fixed it.  I never got an indication in the logs that the DB was the issue I just decided to start with replacing it and then work backward if necessary. 

Thanks for the tips. At least it eliminated the obvious issues.