"Address family not supported by protocol family" error

When ever I try to login to a FTB server it says:

Connection Lost: Address family not supported by protocol family: connect: java.net.SocketException: Address family not supported by protocol family: connect.

What does this mean and how do I fix it?

4

2 Answers

It looks like a Java problem. Try uninstalling Java and re-installing Java again.

This SO answer suggests Java7 may try some (defunct?) IPv6-stuff, which you can apparently disable by adding the switch -Djava.net.preferIPv4Stack=true to your java -jar minecraft.jar call; or more permanently and easier by running the line setx _JAVA_OPTIONS -Djava.net.preferIPv4Stack=true from a command prompt. I do of course assume you already made sure your antivirus is not to blame...