post_permalink not working? [Category Page]

I’m hacking the Category Page plugin (page2cat) to display excerpts and titles to a host of posts at the bottom of each page, but I don’t think my problem is specific to the plugin. I’m having trouble getting the link to the posts to appear. I wrote this:

$catposts = get_posts('category='.$v0."&numberposts=".$limit);
foreach($catposts as $single):
$output .= "<div class='menu_class'>";
$output .= "<a href='";
$output .= $single->post_permalink;
$output .= "'>";
$output .= $single->post_title;
$output .= $single->post_excerpt;
$output .= "</a></div>";
endforeach;

post_title and post_excerpt return like champs but post_permalink returns nothing. I also tried to fake it by doing something with post_ID instead but that also returns nothing. Can we not pull post_permalink out with the same method as that other stuff?