Error -4 occurs when a connection between the computer and AirPort router is blocked.
Try look in the settings for the Windows Firewall for logs of a blocked connection, or in Microsoft Security Essentials for the same thing if you have it installed......to see if you can set up an "exception" or "allow" the connection.
Things would be much simpler if you had an iPhone or iPad handy, or could borrow one for 10 minutes.