Getting email from PayPal regarding my Membership 2 Pro

I am getting the following message from paypal regarding my membership website. Any ideas? Thank you in advance

Please check your server that handles PayPal Instant Payment Notifications

(IPN). IPNs sent to the following URL(s) are failing:

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


Thank you for your prompt attention to this issue.