I did that and tested it again.
It seems like the error occurs when you click to return to the site after payment rather than wait for it to redirect you (from paypal).
You know how after you make your payment, it says "if you are not redirected within 10 seconds, click here" ?
Well, if you wait the 10 seconds, you are directed to the checout_success page like it should do. But if you click to go back (for those who are impatient) that's when they get sent back to the checkout_payment page with the nasty red message.




