@valdes - you are right. This was caused by a change in the Greenfoot API in a newer Greenfoot version. I have fixed the source code now - running the downloaded version should work again now.

Great game! Good effects. The only problem I have is with the controls: I like to move with my right hand, and shoot with my left. Can we have the arrow keys for movement (maybe in addition to wasd) and shooting with SPACE and C or sth like it? I like the explosion effect and sounds!