"Shopping cart is not ready for checkout" error

PRESSERO > *Pressero FAQs
Question: My client is trying to submit an order, but after clicking the payment button, they receive the error message "Shopping cart is not ready for checkout." What is going wrong?
Answer: This error message is given when a product is assigned a different pricing engine between the time that the user added the product to their cart and the time they attempt to check out. Because the pricing that was originally assigned to the cart is no longer valid, the system is unable to calculate the appropriate price for checkout.
This error message is also given if a user deletes an address from their address book after selecting that address as a ship to address for an item in the shopping cart.
Solution: On the shopping cart page, the user should click Edit next to the product. They should review their pricing selections. Then they should click "Add to Cart." They should now be able to check out.
If the error is due to a deleted address, the user can select a new shipping address directly on the shopping cart page.