Hello again,

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When you fire up the Console (typically via "java sim.display.Console"), one thing it does is try to determine all the simulation classes in your system.  These classes are defined in a file called sim/display/simulation.classes and are listed by class name.  Console tries to load each of these classes so it can display them in its list of available simulations.
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Anyway, the #1 reason why Java can't find classes referenced by a simulation class is because it's referring to Java3D stuff and you don't have Java3D installed.  But it's possible that there may be other reasons. 

hm, when I explicitly add j3dcore.jar to the build path of my eclipse project, the error disappears.
That is good, but strange since it worked without this on my Laptop. And I definitely have java 3d installed because the 3D heatbugs start without problems if I start the console via mason\start\mason.bat.
But anyway, I am not really using 3D stuff, so I will ignore this error/bug/warning and get on with my stuff :-)