How can I get marketpress working properly with my theme?

I have installed the marketpress plugin to replace WP-ECommerce. When I look at the site now, there are a few unusual things going on that I have no idea how to fix. 1. When I click on the product page, it shows me an error and then repeats a set number of products infinitely. 2. On the category pages, it takes the first object and lumps it up with no description with the second object. Could you have a look? I have no idea what’s going on.