When working with a Jack Henry application that required the use of a ‘localhost’ reference, it was discovered that the loopback ( address in the HOSTS file seems to be commented out by default in newer OS’s (Windows 2008 R2, Windows 7).  The solution in this case was to just uncomment the entry in the HOSTS file.

MS TECH RESPONSE: At some point in the future, as the world transitions from IPV4 to IPV6, IPV4 will be eventually be disabled/uninstalled by companies that want to simplify network management in their environments.
With Windows Vista, when IPv4 was uninstalled and IPv6 was enabled, a DNS query for an A (IPv4) address resulted in the IPv4 loopback (which came from the hosts file). This of course caused problems when IPv4 was not installed. The fix was to move the always present IPv4 and IPv6 loopback entries from the host into the DNS resolver, where they could be independently disabled."