try replacing the code you gave by this:
// Comments
$sql = "SELECT i.image_id, i.user_id, i.cat_id, i.image_name, i.image_comments, i.image_rating, i.image_thumb_file, i.image_votes, c.cat_name, u.user_name
FROM ".IMAGES_TABLE." i, ".CATEGORIES_TABLE." c, ".USERS_TABLE." u
WHERE i.image_active = 1 AND i.cat_id NOT IN ($cat_id_sql) AND i.cat_id = c.cat_id AND i.user_id = u.user_id $cat_match_sql
ORDER BY i.image_comments DESC, i.image_votes DESC
LIMIT 10";
$result = $site_db->query($sql);
$top_list = array();
$i = 1;
while ($row = $site_db->fetch_array($result)) {
$top_list[$i] = $row;
$i++;
}
$site_db->free_result();
for ($i = 1; $i <= 10; $i++) {
if (isset($top_list[$i])) {
$register_array['image_comments_'.$i] = (check_permission("auth_viewimage", $top_list[$i]['cat_id'])) ? "<a href=\"".$site_sess->url(ROOT_PATH."details.php?".URL_IMAGE_ID."=".$top_list[$i]['image_id'])."\">".htmlspecialchars($top_list[$i]['image_name'])."</a>" : htmlspecialchars($top_list[$i]['image_name']);
$register_array['image_comments_openwindow_'.$i] = (check_permission("auth_viewimage", $top_list[$i]['cat_id'])) ? "<a href=\"".$site_sess->url(ROOT_PATH."details.php?".URL_IMAGE_ID."=".$top_list[$i]['image_id'])."\" onclick=\"opendetailwindow()\" target=\"detailwindow\">".htmlspecialchars($top_list[$i]['image_name'])."</a>" : htmlspecialchars($top_list[$i]['image_name']);
$register_array['image_comments_user_'.$i] = "<a href=\"".$site_sess->url(ROOT_PATH."member.php?action=showprofile&".URL_USER_ID."=".$top_list[$i]['user_id'])."\">".htmlspecialchars($top_list[$i]['user_name'])."</a>";
$register_array['image_comments_cat_'.$i] = "<a href=\"".$site_sess->url(ROOT_PATH."categories.php?".URL_CAT_ID."=".$top_list[$i]['cat_id'])."\">".htmlspecialchars($top_list[$i]['cat_name'])."</a>";
$register_array['image_comments_number_'.$i] = "<b>".$top_list[$i]['image_comments']."</b>";
$register_array['image_comments_thumb_'.$i] = "<a href=\"".$site_sess->url(ROOT_PATH."details.php?".URL_IMAGE_ID."=".$top_list[$i]['image_id'])."\"><img src=\"data/thumbnails/".$top_list[$i]['cat_id']."/".$top_list[$i]['image_thumb_file']."\" width=\"48\" height=\"36\" border=\"0\" alt=\"\" />";
}
else {
$register_array['image_comments_'.$i] = "--";
$register_array['image_comments_user_'.$i] = "--";
$register_array['image_comments_cat_'.$i] = "--";
$register_array['image_comments_number_'.$i] = "--";
$register_array['image_comments_thumb_'.$i] = "--";
}
}