No Shopping Cart Page, But OK in Widget

I made a permalink change to correct a related shopping cart problem (could not have more than one item in cart; fix found on another thread here). But now, the cart items appear okay in the sidebar widget but when you click “Checkout” or try to view the cart as a page, the page does not exist.

I have tried it with other themes with the same result.

This problem did not exist until I made the permalink change.