try changing this code:
<?php
// WA eCart Redirect
if ($PDcart->redirStr != "") {
header("Location: ".$PDcart->redirStr);
}
?>
to:
<?php
// WA eCart Redirect
if ($PDcart->redirStr != "") {
session_commit();
header("Location: ".$PDcart->redirStr);
}
?>