So on the first site I tried to upgrade, I managed to screw up the machine keys.   This problem was promptly addressed and fixed (here) -- So thank you for that very much.

Second site, ready to update- moved machine keys this time, update went without a hitch.  Everyone can log in, all my data is there, everything looks great.

Few days later- it comes to my attention that something I did not even test is broken.  No one can download files.  I have sermons both in doc and mp3 format.  No one can download them.  No one can get PDF files.  Any downloadable files goes to the error: You Do Not Have Permission To View The Requested File

This error shows up on a blank white page with nothing else on it.  I have made no known changes besides the upgrade to 4.3.7.  I have searched both the admin and host menus, and can not find a default security level.  These files should be accessible by anyone.  I don't want people to HAVE to get a login to download these files.  Even my admins can't access them.  I have been able to when logged in as Host, but that's it.

Thanks in advance again for your help!  As always, I'm very impressed with this community and the help available here.

I have fixed it!
I think (someone confirm?) that it's a new feature.

Log in as admin, and go to your Files page.  For each folder that has files listed, you need to update your permissions.  For me, this was setting the permissions to All Users for "View Folder"

This option is below the File Manager area, and you have to set the option for every folder and sub-folder you want to effect.  The settings do NOT propagate to the sub-folders. (at least not that I am aware of)