Marketpress mp_tag_list(); function not working

I can’t get the mp_tag_list(); function to work. I’m trying to bring the product tag list (not the tag cloud) to the sidebar, when in the single product page. Here’s the code I’m using:

<?php mp_tag_list($post->ID, '<div class="product-tags">', ' ', '</div>'); ?>

But nothing happens. Am I missing something?