Hi again!
I have this weird session issue which keeps occurring - not sure if you've encountered it before but I thought I'd give it a shot anyway.
The product adds to the cart fine, however when going to Paypal, the foreach error (nothing in cart) comes out.
Upon further investigation, it seems like the session gets cleared off the moment any files in wp-content is accessed.
I've got a var_dump($_SESSION]); tested on the root and on wp-admin and it works fine - only when it's tested in wp-content, it gets cleared off.
Any idea on how to counter this?