Marketpress Category Filter Not Working - No products appear

Hi,
This is regarding our Organics4Seniors site. I've just removed Nathan Om's old Pro Theme (which I've been putting off doing for a long time now), so I've now updated to the latest version of Marketpress and I'm just using Simplemarket with it. I have all the products and categories still entered but when a category is selected from the filter or the sidebar widget listing the categories, no products appear on the page. I've checked everything three times and can't figure out what the problem is. I need help! I've enabled support access for you, but the site requires a login, so let me know and I'll email it to you.
Thanks,
Sherry