Marketpress: Page is empty after adding a product

I have just updated the plugin to the latest version 3.1.1. Now when I add a product to the cart, the redirection to the shopping cart does not work. The product list page reloads but it is empty! Why is this happening? If new versions are released, they are supposed to work fine. Actually they seem buggy.
Sorry but this is not what a user should expect.
Can you please check on the site?

Thanks in advance,