Cart not working in Marketplace

Customers can't complete transactions due to a number of issues:
1. When adding something to cart, it just continues to say "adding", if you refresh the page, it puts the item in the cart.
2. When you click on the cart to check out, the "continue as guest" button is unresponsive
3. When you try to check out, they get the attached message, even if fields are filled.
I created a test item for $1.00.