From a session and cart perspective the www. and domain only version of the site have completely separate data. The solution is usually to add an .htaccess rule to force people to always view the site either with or without the "www." in the url and then make sure you are referring to it correctly in the paypal settings on the confirm.php page.
Well, doggone it! You are absolutely correct. I modified htaccess to force www and the checkout worked like a champ.
Thanks so much for the easy fix.