Lösung:
install/installer/full.php bearbeiten.
Eintrag Zeile 773,774
$transaction->addQuery("INSERT INTO `".PREFIX."user` (`userID`, `registerdate`, `lastlogin`, `password`, `password_hash`, `password_pepper`, `nickname`, `email`, `email_hide`, `email_change`, `email_activate`, `firstname`, `lastname`, `sex`, `town`, `birthday`, `facebook`, `twitter`, `twitch`, `steam`, `instagram`, `youtube`, `icq`, `avatar`, `usertext`, `userpic`, `homepage`, `about`, `pmgot`, `pmsent`, `visits`, `banned`, `ban_reason`, `ip`, `topics`, `articles`, `demos`, `files`, `gallery_pictures`, `special_rank`, `mailonpm`, `userdescription`, `activated`, `language`, `date_format`, `time_format`) VALUES
(1, '".time()."', '".time()."', '', '".$adminhash."', '".$new_pepper."', '".$adminname."', '".$adminmail."', 1, '', '', '', '', 'u', '', '0', '', '', '', '', '', '', '', '', '', '', '', '', 0, 0, 0, NULL, '', '', '', '', '', '', '', 0, 0, '', '1', '', 'd.m.Y', 'H:i')");
Zu
$transaction->addQuery("INSERT INTO `".PREFIX."user` (`userID`, `registerdate`, `lastlogin`, `password`, `password_hash`, `password_pepper`, `nickname`, `email`, `email_hide`, `email_change`, `email_activate`, `firstname`, `lastname`, `sex`, `town`, `birthday`, `facebook`, `twitter`, `twitch`, `steam`, `instagram`, `youtube`, `icq`, `avatar`, `usertext`, `userpic`, `homepage`, `about`, `pmgot`, `pmsent`, `visits`, `banned`, `ban_reason`, `ip`, `topics`, `articles`, `demos`, `files`, `gallery_pictures`, `special_rank`, `mailonpm`, `userdescription`, `activated`, `language`, `date_format`, `time_format`) VALUES
(1, '".time()."', '".time()."', '', '".$adminhash."', '".$new_pepper."', '".$adminname."', '".$adminmail."', 1, '', '', '', '', 'u', '', '0000-00-00', '', '', '', '', '', '', '', '', '', '', '', '', 0, 0, 0, NULL, '', '', '', '', '', '', '', 0, 0, '', '1', '', 'd.m.Y', 'H:i')");
Nach dieser Änderung funktioniert die Installation.