Paypal failing on confirm to own website - but only for some users/shipping info not transferring
I have asked a number of people to test that my setup to Paypal Express Checkout is working - after a lot of moving and adjusting of code it works for me on all browsers, works for one other person on IE and FF, correctly ending on checkout_success.php, sending the confirmation email and inserting data into the orders table.
For everyone else, the process fails after they have successfully completed their details on PayPal and click continue to redirect to the originating website for completion, where it ends on cart.php with the message "cart is empty" - which suggests to me that it's not the paypal transaction that's failing, but something in eCart.
I'm beyond frustrated as I can't see how it can be a browser or server issue when it works perfectly for some and not for others.
Secondary (?) information, which also needs to be resolved - shipping information is not prepopulating paypal shipping form (not that I can find out whether it is even supposed to), nor is it showing on confirmation page or email. I have changed form field bindings to pre-populate with database info after users login, and wonder if that is the issue there.
I'm already a week overdue with this job and a speedy resolution would help a lot - thanks.
Checkout pages are attached privately.