Address Family Not Supported by Protocol Family

Problem

I have experienced the following error: "Address Family Not Supported by Protocol Family; Connect". How do I solve it?

Cause

This seems to be an IPv6 connectivity problem. By default, the Java runtime used by Oxygen XML Author Eclipse plugin prefers to create connections via IPv6, if the support is available. However, even though it is available in appearance, IPv6 sometimes happens to be configured incorrectly on some systems.

Solution

A quick solution for this problem is to set the java.net.preferIPv4Stack Java property to true (java.net.preferIPv4Stack=true), by following this procedure:

Create a file named custom_commons.vmoptions and on a single line, add -Djava.net.preferIPv4Stack=true. Then save the file and copy it to the Oxygen XML Author Eclipse plugin installation folder (may need admin access).
Restart Oxygen XML Author Eclipse plugin.
Make sure the procedure was successful by going to Help > About > System properties and check that the value of the java.net.preferIPv4Stack property is true.