Yep, EricTheGray has it correct.
Some of the site features are using separate databases, thus requiring separate registrations/logins.
TIP: Register with and use the same username/password across different site features requiring such.
The old site had everything integrated into 1 database. Very convenient...but the server had a catastrophic failure and the single database for the site was corrupted, along with its backup.
So, I opted to have separated databases when I can; inconvenient but best to not have all assets in one place. I'm still going to try and see if I can pull anything out of the old database, lots of great content there. I'm awaiting a forensic computer buddy of mine to return from the holidays for his attempts to recover.
The good thing: the server failure/crash occurred during the Xmas holidays so I had time to resurrect the site.
The bad thing: the server failure/crash occurred during the Xmas holidays and I had to spend time to resurrect the site