Existing duo accounts should now be fixed and new duo accounts can be made correctly now.
If you've recently made a duo account and it failed to log in, change the password on
http://accounts.mania-exchange.com/ (of the duo account) which will fix it. New duo accounts should not have to follow this procedure, though.
If you're still affected by the issue that you get the server error as shown in the screenshot at the initial post, clear the cookies of tm.mania-exchange.com and you can log in again.