paypal notification

I have received this message from Paypal:

Hi Penelope Vingoe, Please check your server that handles PayPal Instant Payment Notifications (IPN). IPNs sent to the following URL(s) failed:

http://www.clayaround.com/shop/pp.phtml

If you don’t recognise 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.

The host to my site says “I think the return url the cart is telling paypal to use is not working”

The customer paypal payments are coming through to my paypal account.

Would you kindly advise?

The page I need help with: [log in to see the link]