2checkout order problem

I have been trying to get 2checkout working but there is one major problem

When payment has been made the order is logged in the opencart backend, however the payment is taken successfully by 2 checkout

i have followed the instructions here to the letter - https://www.2checkout.com/shopping-cart/open-cart/


When the customer is redirected to /index.php?route=payment/twocheckout/callback it just stays on that url showing a blank page.

I am using opencart 1.4.9


Does anyone know how to fix this?

Thanks