We are getting this message from paypal and payments are now failing (although everything was working fine for the last month)
Please check your server that handles PayPal Instant Payment Notifications (IPN). IPNs sent to the following URL(s) are failing:
http://[www.OURCLIENTSURLISHERE]/shop/paypal/standard/ipn/
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.
any help or other messages about how to resolve this would be appreciated we are using magento shopping cart