For security I can't do that I'm afraid as that would show my API and Payment configurations.
The configuration is standard WA eCart and I have not amended the script. However as I am using SSi's the page checkout.php becomes index.php?mod=checkout.php and I believe herein lies the issue. The page is trying to submit to itself for the Paypal via:-
<form name="PayPal_ExpressCheckout_form" action="<?php echo $_SERVER["PHP_SELF"]; ?>" method="post">
But this can't be the case as the file checkout.php is an include.
I think I need direct WA Support on this, but any other insights are appreciated.