[Plugin: HeadSpace2] Great, but I have an error for meta keywords for category pages!

Hello,

Great plugin, but I have a problem with the meta keywords for the category pages.

For pages and posts I create custom fields and uses a code like this:
<meta name="keywords" content="<?php $key="keywords"; echo get_post_meta($post->ID, $key, true); ?>">

On my category page it simply shows the latest post’s metakeyword.

How should my <meta name=”keywords” content=”???”> look like?

Thanks in advance,
Jonas