Old disabled shopping Cart - I get these notices: PayPal Instant Payment Notification Warning

[jrr_com]

I migrated to a new shopping cart from an older one (oscMax) over a year ago, and have just started to get these messages from PayPal "

Please check your server that handles PayPal Instant Payment Notifications (IPN). IPNs sent to the following URL(s) are failing:
https://www.flippers.com/catalog/checkout_shipping.php

I had left that old cart up, but disabled, until recently when I deleted it. then the above email messages from PayPal started to come.

I am using PayPal on my new store (OpenCart) and don't want to risk damaging the links to it.

I did see the post about stopping IPN notifications, however PayPal has since changed the interface and the advice is useless as the links it says to use no longer are valid.

I can't find any obvious way to access links in PayPal to tell it to stop checking the old cart...

Suggestions are appreciated!

Thanks!