Paypal Express IPN Failing

I switched to Paypal Express and ever since then all of my transactions are showing up as a failed IPN transaction. I get paid and the orders are completing properly in the cart but I have started getting warning emails from Paypal.

The ipn_main_handler.php file is still in the right place and the only thing that changed was the switch from Paypal standard to Express. Can you point me in the right direction? Thanks.

I have started getting warning emails from Paypal.

Can you point me in the right direction?
Would hrlp to know what the actual issue is?

Sorry about that. Here's the note from Paypal:

Please check your server that handles PayPal Instant Payment Notifications (IPN). IPNs sent to the following URL(s) are failing:

https://mysite.com/ipn_main_handler.php

If you do not recognize this URL, you may be using a service provider that is using IPN on your behalf. Please contact your service provider with the above information. If this problem continues, IPNs may be disabled for your account.

Thanks.

Without more info this is just guessing

Go to your ZenCart admin > tools > version server info

Search for "curl"

Also, in the setup for the payment module enable logging and the logs should have additional information

Double post error

What version of Zen Cart?

Not sure if this will help you but I had a similar issue and it turned out to be file /includes/languages/english/checkout_process.php was corrupt. I replaced it with an archive and the problem was solved. I was able to determine this by following the advice of DrByte and reading through the log file in the cache directory.