Paypal automatically shut off my IPN's because the status was showing to them as failed. However, my website was receiving the IPN's.

I called Paypal and they said that they disabled the IPN because the status was coming back as failed. Is there a reason that the status would be listed in Paypal as failed for the IPN, when it was successfully transmitted to the website? Is there something that I would need to change in the settings to make that succeed?