Marketpress - shortcodes help

I am trying to set up some shortcodes for my site which is a multi-site with marketpress installed.

Anyway rather than categories I will be using tags for the products, so that I can add a shortcode to different pages and display various products.

Anyway this is what I have

[mp_list_products page="1" per_page="5" tag="fathers"]

And it doesn't work, am I doing something really stupid here?