Unable to reach ArcGIS Server 10.1 Configuration Manager

For web GIS application installs behind a firewall (intranet) ArcGIS Server communicates with HTTP port 6080 by default (Ports used by ArcGIS Server).  Typically you can navigate to your server local host or loopback IP address of port 6080 to reach the ArcGIS Server Configuration Manager (similar to shown below).

http://localhost:6080/arcgis/manager
http://127.0.0.1:6080/arcgis/manager

But what if the page errors out and you cannot reach the ArcGIS Server Configuration Manager? 

There could be many things causing this problem which are relatively simple to correct, but not always simple to diagnose.  Here are a few recommendations to help diagnose and correct this problem:

1.      The first and most obvious item to check is your Windows Network Diagnostics.  Troubleshooting with Windows Network Diagnostics might help reveal the underlying issue.  You might get an error message like: "The remote device or resource won't accept the connection", or “The device or resource (127.0.0.1) is not set up to accept connections on port “6080”.  (shown below).

This type of error is indicative of an implicitly blocked port or similar issue.  The fix could be as simple as adding an exception to your firewall for port 6080 (TCP).  If that fixes it, great!  If not, read on…

2.       A second item to check would be the "Hosts" file.  In very rare situations this could be the culprit.   Perhaps some network configurations were made or you encountered network problems elsewhere since initially installing ArcGIS Server.  The "Hosts" file could be pointing to an improper IP address, instead of  the desired one.  If this is the case, simply alter the IP address in the "Hosts" file to point back to your local host or loopback IP address for port 6080 and it should be repaired.

Of course there could be many other reasons you are having problems, but since the documentation on this subject is limited, I figured it would be worth sharing some of the solutions we have used.  Hopefully you find this helpful.