Are you behind a fire-wall or a
severe proxy server?

In this case it may happen that your computer cannot run Java applets. In oder to solve the problem, you - or your system administrator - may modify the security settings in a particular way. Here's the description for Netscape Communicator 4.0.

The modification necessary:

You can modify Communicator preferences "manually" by editing your
Preferences file.

The name and location of this file varies from platform to platform:

   On Windows 95 and NT, \Program Files\Netscape\Users\\prefs.js
   On UNIX, ~/.netscape/preferences.js
   On Macintosh, "System Folder:Preferences:Netscape f:Netscape Preferences"

Be sure to edit this file only while all instances of Communicator are shut
down, as Communicator will overwrite prefs.js when it exits.

To enable the preference, add this line to the Preferences file:


The explanation therefore:

When a Java Applet attempts to "phone home", or make a socket
connection to its originating host, Communicator will first
perform a DNS lookup to prevent certain "spoofing" attacks.
In some intranets, DNS lookup for external hosts is disabled,
and all external traffic goes through a proxy. In this situation,
the applet will normally fail to make the desired connection.

With this preference enabled, if the lookup fails, then textual
name equivalence is used to determine if the class can make a
connection. This option causes the "name of the home" to be relied
upon rather than the stricter DNS/IP address.

This is one of the few "hidden" security preference which end users
in some intranets may need to enable.

We thank Wolfgang Michael Terenyi (Novartis, Parents community of the Academic Gymnasium Wien) for solving the problem.

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