It appears that the database query handling the account registration did not return any results.
Check the "./modules/account/create.php" file:
// Woohoo! Register ;)
$result = $server->loginServer->register($username, $password, $confirm, $email, $email2, $gender, $birthdate, $code);
if ($result) {
...
}
else {
exit('Uh oh, what happened?');
}
Check the database "login" Table. Do you see the newly registered account?
Make sure the FluxCP software has access to the database "login" Table, and that the associated MySQL user holds the appropriate privileges.