You never removed the form action on line 224 of your cart.php page. You need to do that first.
It looks like you didn't enter the url to the checkout page correctly when applying the pass session to site server behavior.
On line 10 you have:
$sessionPassTo = "http://www.newdomain.com/receive_session.php";
it should be:
$sessionPassTo = "https://secure.browngrotta.com/checkout.php";
And it looks like you never applied the receive server behavior on the checkout page at all...
on your checkout.php page apply the server behavior: eCart->General->Recieve Passed Session