garyclemens:
I installed the IPN module well over a year ago there is a patch release for any one using zencart version 1.3.7and before. This can be down loaded here:
http://www.zen-cart.com/forum/showthread.php?p=390776#post390776
Its easy to tell if you need this patch. If you do not have a field for Payment Data Transfer Identity Token in the paypal ipn module you will need to do this upgrade. The field to enter this is is located at modules>payment, click on paypal ipn then edit. If its not there that is your problem.
You will also have to enable Payment Data Transfer in your PayPal account. When you do this you will receive your token.
That is good info. A while ago (and a couple of Simple Seo version back) I had similar IPN problems as described here. I do not need the Payment Data Transfer patch because I can see the "Payment Data Transfer Identity Token" field in Paypal module. However, that field is blank.
Are you saying that in order to use Simple SEO URL, I have to use PDT Token? Because shop is working fine without PDT token now (albeit without the Simple Seo). Or should I give the lastest version of Simple SEO a try again due to some changes in the Seo module?