Dear Luke,
Unfortunately, this is a problem that occurs when a different JRE version is used than the JDK version with which the tutorial was built with. It seems that JavaFX is completely unstable in this respect. We plan to create a package which will then ship directly with the precise version of the JRE version that is working properly. So as soon as you do not work with the tutorial but the libraries on your own project, the problems should not occur again.
Sorry for not having better news about your crashes.
Best regards,
Andreas