Yes, I did everything in that tutorial. There is one difference, though: the shortcode button at the top of the tutorial has a slightly different format, while what I use is what is on the plugin settings itself "[wp_cart_button name="Test Product" price="29.95"]" Which should be used?
The page is http://madlom.org/index.php/test-paying/
It's only accessible through a direct link, as I have not yet turned this on since it doesn't work yet.
There are no caching plugins installed. I have also tried this with all plugins deactivated and still had the issue. Plugins are: Akismet, Auto ThickBox Plus, Comprehensive Google Map Plugin, Contact From 7, EWWW Image Optimizer, Google XML Sitemaps, jQuery Updater, WordPress Importer and this shopping cart. Pretty straightforward stuff.
Thanks for the speedy response and your help.