Paypal Instant Payment Notification Warning

I got this email from Paypal:

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


http://www.1stplacepix.com/sy-inc/store/payment/paypal-standard-return.php http://www.alliancephotos.com/sy-inc/store/payment/paypal-standard-return.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. 


Thank you for your prompt attention to this issue.

I saw that another user had their IPN disabled. Why am I getting this issue?

What version of sytist are you running?

Most likely the case since your URL does not include httpS.