title: PayPal IPN postback failure
body: <p>I have recently upgraded my Magento live website from 1.6.2.0 to 1.7.0.0.
  Starting after the upgrade, I now have a issue in PayPal Standard Payment.
  When a customer pays by using PayPal, the payment on PayPal goes smoothly, but the Magento order state is not updated and stays in "pending" state.</p>
  
  <p>I have checked various websites reporting this, but I can't still solve the problem.</p>
  
  <p>I have the payment_paypal_standard.log reporting this:
  "....
  [postback_result] => 
  [exception] => PayPal IPN postback failure. See paypal_unknown_ipn.log for details."</p>
  
  <p>But I have no paypal_unknown_ipn.log being created, so I can't have more info about the error.</p>
  
  <p>Investigating more, I have found the possible trouble is that the returning PayPal postback string is not correctly decrypted, but I have not found a real solution that help me to solve the problem.</p>
  
  <p>Is there a way to find a solution shortly?
  Thank you all in advance.</p>