Checkout goes nowhere

Hello,
I have a site on wordpress called ProBubbles.com

I have installed the Paypal Ultra Simple Shopping Cart Plugin and it works until I click on the “checkout” and nothing happens. At this point it is supposed to take my customers to paypal so that they can checkout with all the items in the cart but it does nothing.

I called paypal and they say this may be something that wordpress does when it updates their code, and that there is away to turn off these updates. Can you please help me with this?

Thank you,
Jason

http://wordpress.org/plugins/wp-ultra-simple-paypal-shopping-cart/