Hi,
I already use the PDT Identity Token for another script (DLGuard) It doesn't seams possible to have more than one PDT Identity Token at Paypal. according to your more information help, you are mentioning "The result is that the Auto-Return URL configured from within your PayPal® account, becomes the default, which is then overwritten on a per-transaction basis."
Does it means that I leave the PayPal® PDT Identity Token box empty ?....