I am having the same issue with 2checkout. Sometimes I have gotten the "you don't have cookies enabled" return once putting both a demo, and live payment through 2checkout. As far as I know, the checkout_success.php page handles both the parameters and thank you message, am I wrong on this? I tried adding 255 character output to the page as well as adding a base href at the top of the php file, but neither have worked. I'm very interested in a fix for this, otherwise I will have to go with the manual redirect (it works fine for me). On a side note, products are not being created in the 2checkout database when they are passed through. Any ideas on this anyone?