Initial user was not created by installer
Fragment of a discussion from Project:Support desk
Meh, probably just be easier to add:
$wgAddGroups['user'] = true;
to the bottom of your LocalSettings.php, then log into your wiki as that user, and use special:userrights to add yourself to the Sysop (Administrator) and bureaucrat groups. Then make sure to remove that line from LocalSettings.php, and you are all set (Its very important to remove said line from localsettings.php afterwards, as it allows anyone to change group permissions).
p.s. See Manual:$wgAddGroups for info on what the above actually does.
