I wonder if the download of the JRE failed and you only have a partial copy stored on your system. That might explain the extraction error.
Check the C:\Users\robot\wpilib\tools folder on your system and verify that you see a file named ejdk-8u6-fcs-b23-linux-arm-vfp-sflt-12_jun_2014.tar.gz and that it is 121,568,917 bytes long. If it isn't try deleting the file and repeating the process to see if you can get a good download.
If that doesn't work, the
http://wpilib.screenstepslive.com/s/...ller-java-only page may provide some clues as to how you might find an alternative way to download the file.
Good luck.