So, me and my friends wanted to get back to minecraft and i'm the "responsible" to create our server. I found you guys and tried to use it but when i followed your tutorial i came with that error when trying to launch.
I'm using TLauncher-MCL to launch the game because i used to use it with my bf (to play local) but if you have any other suggestions of better launchers i'm totally ok with doing it.
I hope this helps...also, im on windows 10 (i dont know if that helps)