[Plugin: WP e-commerce] ajax error

I have setup wp e-commerce on my site, and created some products and such, but when I go to add anything to the basket, nothing happens on the front end. With Fancy Purchase Notifications on, the Updating window appears, and then… nothing. If I refresh the page, the shopping cart has been updated.

Similarly without the Fancy Purchase Notifications on, when I hit the add to cart button, nothing happens. But again, if I refresh the page, then the shopping cart has been updated.

Anyone have any ideas?

Thanks,