Now I'm just being returned to an empty cart and no update in the database with a new order...
If I try it a second time, it's going to checkout_failure.php page; so not only is this not successful, but it's still going to the wrong failure page. If I put the error code request on each page, the results for PayPal Full Response are empty.
I've replaced fresh copies of:
cart.php
checkout_failure.php
checkout_success.php
checkout.php
confirm.php
pp_cancel.php
pp_checkout_failure.php
pp_checkout_success.php
pp_confirm.php