Hiya, As others have pointed out, this doesn't run at the moment, the exact error I'm getting is: java.lang.NullPointerException at greenfoot.util.GraphicsUtilities.toCompatibleTranslucentImage(GraphicsUtilities.java:274) at greenfoot.util.GraphicsUtilities.loadCompatibleTranslucentImage(GraphicsUtilities.java:221) at greenfoot.GreenfootImage.loadURL(GreenfootImage.java:143) at greenfoot.GreenfootImage.loadFile(GreenfootImage.java:167) at greenfoot.GreenfootImage.<init>(GreenfootImage.java:70) at checkerun.act(checkerun.java:22) at greenfoot.core.Simulation.runOneLoop(Simulation.java:200) at greenfoot.core.Simulation.run(Simulation.java:129) NullPointerExceptions often occur when you haven't initialised something properly - i.e. you're doing something with a variable that contains null (is empty.) But apart from that, there's not much anyone can do unless you upload the source code (it's via a check box in the export dialog.)

Go into the Java control panel, navigate to the advanced tab and make sure either show console or hide console is checked (as long as it's not never show console.) Also make sure you have the option set to get the java coffee icon in your taskbar when a java application launches. If you selected show console it'll open automatically (which I find dead annoying.) If you selected hide console then just right click on the icon and select show console when you want to see it (if the simulation stops suddenly when you don't expect it to, that's usually a good sign that an error's occured.)

It might have something to do with the message it throws when you start it sun.plugin2.main.client.PluginMain: unrecognized message ID 46 Buuuuuuut the only way to know for sure is to see the source code (hint hint)

Hmm, I don't get that message. Just the NullPointerException when it crashes. Either way though, as has been said already, it's all going to be guessing games without the source to look at. Feel free to upload it here or over on Greenfoot discuss, and then whoever gets there first will take a look!