Hello, same here, exactly the same problem. It says "Exception in thread "JavaFX Application Thread" Exception in thread "main" java.lang.UnsupportedClassVersionError: b4j/example/main has been compiled by a more recent version of the Java Runtime (class file version 53.0), this version of the Java Runtime only recognizes class file versions up to 52.0". JDK is OpenJDK 11 + OpenJFX 11 as said on the B4J Download page, JRE is most recent.