Well... No thanks for any help here. I figured out how to fix it myself. I imagine one or two files were corrupt, but didn't know what to delete. My fix was far from elegant, but I am up and running. I created a clean new profile, then copied all the files from a backup over that profile. Unfortunately those files were from July. (my automatic backup was not working correctly) I was able to open Thunderbird and all the mail folders were back and my settings were back. I then copied the "Mail" folder from the profile from my current non-working profile into the new profile. Everything is working now.