That indicates you have a Common Notification URL (in Seller Admin > Account Preferences) and/or a Payment Variable Information URL (in the settings of an individual product ordered in that transaction) which did not respond when we attempted to POST the order data to it.
If you recently added those settings, you might want to double-check them to make sure they are complete and correct URLs starting with "http://"; also, since those fields already include an "http://" by default as a hint before you paste anything in there, make sure you haven't inadvertently doubled that part ("http://http://...") when adding your own URL.
