I am having the same problem with paypal but the cart is working fine. I tested sessions by adding to the cart, then deleting all sessions files – and seeing the cart is reset.
I added print_r($_SESSION); to the wp index file and the eStore_payment_submission.php file – it shows the cart contents on all pages, but it does NOT show on the eStore_payment_submission.php page, no matter what I try, Weird huh.
Disabled all plugins, switched to the base theme and tried a bunch of debugging tricks but still no joy. The session is not loaded for the submissions page.
Any suggestions?
edit: actually is only shows
Array
(
[eStore_custom_values] =>
)