SimEvent subclass MUST be in *.cc : why?

After a little bit of reading on the subject, I added a simEvent to my program (below). I initially posted both code snippits in myClass.h, and they resulted in the following 4 compiler errors (ms-vc6).

The fix was to move the simEvent subclass AND the simBase.h include to myClass.cc. Could someone please explain why?

Thanks,
RavenSlay3r

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