What is the ID on your file:
/admin/includes/category_product_listing.php
Do you see code in there similar to:
<?php
// bof: categories meta tags
if (zen_get_category_metatags_keywords($categories->fields['categories_id'], (int)$_SESSION['languages_id']) or zen_get_category_metatags_description($categories->fields['categories_id'], (int)$_SESSION['languages_id'])) {
echo '<a href="' . zen_href_link(FILENAME_CATEGORIES, 'cPath=' . $cPath . '&cID=' . $categories->fields['categories_id'] . '&action=edit_category_meta_tags') . '">' . zen_image(DIR_WS_IMAGES . 'icon_edit_metatags_on.gif', ICON_METATAGS_ON) . '</a>';
} else {
echo '<a href="' . zen_href_link(FILENAME_CATEGORIES, 'cPath=' . $cPath . '&cID=' . $categories->fields['categories_id'] . '&action=edit_category_meta_tags') . '">' . zen_image(DIR_WS_IMAGES . 'icon_edit_metatags_off.gif', ICON_METATAGS_OFF) . '</a>';
}
// eof: categories meta tags
?>