it is cos you need todo some custom edits for your theme
if you add this
function show_facebook()
{
global $settings, $user_info, $context, $txt, $modSettings;
if ($context['user']['is_logged'] && !empty($modSettings['fb_enable']))
{
if (!empty($user_info['fbname']))
echo '<img src="' . $settings['images_url'] . '/facebook.png" alt="'.$txt['fb_title'].'" /> <a href="#" onclick="javascript:fbLogincheck(); return false;">'.$txt['fb_title'].'</a>';
else
echo ' <img src="' . $settings['images_url'] . '/facebook.png" alt="'.$txt['fb_title'].'" /> <a href="#" onclick="javascript:fbLoginsync(); return false;">'.$txt['fb_integrate'].'</a>';
echo'<br /><br />';
}
elseif (!empty($modSettings['fb_enable']))
echo'<a href="#" onclick="javascript:fbLogin(); return false;"><img src="http://b.static.ak.fbcdn.net/rsrc.php/zB6N8/hash/4li2k73z.gif" alt="" /></a>';
}
before // The main sub template above the content.
the error will go away