What symptoms are fixed by this code?
I am having a problem with paypal express as well. I've implemented the code in this thread, and was able to have success on my PC.
However, my client performed a test and got the same error we've been having.
After clicking the express paypal link, the user is routed through the Paypal screens to select payment source and confirm payment. Then they should be brought back and presented with the pp_confirm.php, but instead they are ending up at cart.php with the message that their shopping cart is empty.
They do not end up at a checkout failure page, but the transaction does not go through. How can I check the request / response information to and from paypal?