I'm sure, that it has worked after installing the board.
I just changed the general configuration, template, smilies, chat mod, something in user's/group's rights, general group & rank stuff and the right to view/write etc. forums.
I haven't changed anything in phpMyAdmin, except for deleting two users from the user-table.
By the way: the users are being registered, but instead of confirming the registration and sending an email, that error message appears.