Mart, the Session("OrderID") and Session("OrderDetails") objects aren't values passed by a payment gateway, they are local session objects set by Kartris (or supposed to be).
For ecommerce tracking to work Kartris would have to set these objects in the Checkout.aspx page, and read them back in the CheckoutComplete.aspx page, according to the code.
They are not passed through the payment gateway.
But they are not set by Kartris, hence the object doesn't appear, hence no e-commerce tracking.
It isn't really anything to do with PayPal, this is to do with Kartris.
Why are these vital session objects not set? And how can we solve it?