its in there..
// Is the user allowed to administrate at all? ([admin])
if ($context['allow_admin'])
echo ($current_action == 'admin' || $context['browser']['is_ie4']) ? '<td class="maintab_active_' . $first . '"> </td>' : '' , '
<td valign="top" class="maintab_' , $current_action == 'admin' ? 'active_back' : 'back' , '">
<a href="', $scripturl, '?action=admin">' , $txt[2] , '</a>
</td>' , $current_action == 'admin' ? '<td class="maintab_active_' . $last . '"> </td>' : '';
what happens if you go to your forum, and put ?action=admin on the end of your main forum's URL?