That is actually a slight mistake, LGM should not have output that message. I have already patched it in the master branch, it looks like that change was accidentally made within the last year. It is really just a warning to tell people that some function we use somewhere in the IDE may not be supported by your Java version (like how we don't support Drag and Drop on the main tree in < Java 6) so ignore for it right now. I am going to be patching some other things and then updating LGM again.
https://github.com/IsmAvatar/LateralGM/pull/278https://github.com/IsmAvatar/LateralGM/pull/279Can you actually run that script one more time and let me see the output? There's two dependencies there that got updated but I don't think they should have been updated or needed to be.
At this point though I really do think your issue is entirely the Java installation. Could you boot a live CD of Lubuntu and see if it works there?