Had to reinstall vSphere vCenter server today due to a sudden power loss that corrupted the SQL database. I was able to log in with the firstname.lastname@example.org account, and added a 'root' admin account in the vSphere web client. Then added it to the administrator group.
I can't log in with that account through the older vSphere Client. Not sure what I'm missing. Everything is at 5.5 currently.