Paypal IPN script troubleshooting (PHP)

Hello, I have a PHP script that automatically sends orders from my Paypal customers (through IPN -- [login to view URL]) to my shipping company ([login to view URL]). This script has worked great. However, I recently tried to set up "Shipping Methods" inside my Paypal account. (See screenshot attached) After I set up the shipping methods (for example, to charge international customers extra shipping charges), the script no longer worked. I reverted the settings to the previous settings, and the script worked again. I need an experienced PHP/XML programmer to take a look at the script and figure out why this happens. I would like to use the Paypal shipping methods feature -- however, again, it causes the script to fail, for some reason. If you have had experience with Paypal IPN, that is best! Let me know your bid for this project. Thank you, Keith