I had that error show up for me once or twice but then it went away on my end. I've had no problems being able to login nor have I had anyone complain about not being able to login.
I've double checked the database settings in the config-inc.php file and they are correct. I've also double checked #83 in the settings table and it's showing the proper vbulletin database prefix.
One thing I did just notice, in phpmyadmin, #84 says I'm running pversion 5.11. In PP admin, the update announcement is showing saying "PhotoPost 5.13 Security Update Now Available!" but then under that it says Current Version 5.13.