I am sorry, but after carefully looking over your code, I do not see anything that could be the cause of the aforementioned error. I wish that I could be more helpful on this matter.
java.lang.IllegalArgumentException: Could not open sound file: New Folder at greenfoot.sound.SoundExceptionHandler.handleIOException(SoundExceptionHandler.java:66) at greenfoot.sound.SoundFactory.createSound(SoundFactory.java:115) at greenfoot.sound.SoundFactory.getCachedSound(SoundFactory.java:130) at greenfoot.sound.SoundFactory.<init>(SoundFactory.java:67) at greenfoot.sound.SoundFactory.getInstance(SoundFactory.java:77) at greenfoot.export.GreenfootScenarioViewer.init(GreenfootScenarioViewer.java:180) at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source) at java.lang.Thread.run(Unknown Source) Caused by: java.io.FileNotFoundException: Could not find file: New Folder at greenfoot.util.GreenfootUtil.getURL(GreenfootUtil.java:532) at greenfoot.sound.SoundFactory.createSound(SoundFactory.java:95) ... 6 more
java.lang.NullPointerException at greenfoot.core.ProjectProperties.load(ProjectProperties.java:93) at greenfoot.core.ProjectProperties.<init>(ProjectProperties.java:82) at greenfoot.export.GreenfootScenarioViewer.init(GreenfootScenarioViewer.java:152) at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source) at java.lang.Thread.run(Unknown Source) Exception: java.lang.NullPointerException
private GreenfootSound one = new GreenfootSound("unbreakable.mp3");