In archive, meta description and keywords are empty ?

[Mean]

In archive/index.php

$metatags = "<meta name=\"keywords\" content=\"$threadinfo[title], " . $vbulletin->options['keywords'] . "\" />
<meta name=\"description\" content=\"[$vbphrase[archive]] " . ($p > 1 ? construct_phrase($vbphrase['page_x'], $p) . " " : "") . "$threadinfo[title] $foruminfo[title_clean]\" />
";

But something is wrong and why are they empty ?

For example:
http://www.forumistan.net/archive/al...ati-t4946.html

<meta name="keywords" content="" />
<meta name="description" content="" />

How can I fix this ?

--------------- Added [DATE]1200835339[/DATE] at [TIME]1200835339[/TIME] ---------------

Please can you help me ?...