We did this and I was supposed to put you on the phone with Wm after we spoke: it still doesn't work. He now is getting a #13 error "merchant login or id is invalid" when hitting process payment on checkout.php...He says our ID is not invalid. How do we fix this? Maybe you could call and talk to him if you don't think replying to this post will be clear enough.
OK, we figured it out. Had to reenter our login ID, it was still set to your sandbox account. Didn't notice that when i changed it on Friday. eekends can be very rejuvenating! So no answer needed!