[JBWeibelt]

In this Function

function parseBbCode($bbcode, $limit = 0)
{
  global $db, $vbulletin, $vbphrase, $vboptions;
  require_once(DIR . '/includes/class_bbcode.php');
  $parser =& new vB_BbCodeParser($vbulletin, fetch_tag_list());
  $text = $parser->do_parse($bbcode);
  if($limit != 0) {
  	if(strlen($text) > $limit)
  		$text = substr($text, 0, $limit).' ...';
  	}
    return $text;
}

it's this line

$parser =& new vB_BbCodeParser($vbulletin, fetch_tag_list());

The error seems to only be present in the Classifieds tab is selected.