Wait – you should be able to just open the backup and just upload the Theme My Login folder to /wp-content/plugins. That’s how I restored it. If, for some reason you can’t get version 6.4 back, I can send it over (I can’t seem to find an archived version on Jeff F.’s site for this version!).
Rolling back to 6.4 works. We gotta be rollin’ in our 6.4’s.
It seems to only affect some sites, as other sites we have on 6.4.1 are working fine. Not sure what the issue is, but going to be cautious with updating to 6.4.1 for other sites we have.