FitNesse. UserGuide.
FitNesseWontStart [add child]

What to Do If You Have the Wrong Java Runtime Environment

FitNesse requires version 1.5 or later of the Java Runtime Environment (JRE).
If you see the messages:

C:\fitnesse>java -jar fitnesse.jar
Exception in thread "main" java.lang.NoClassDefFoundError:
at fitnesse.FitNesse.parseCommandLine(Unknown Source)
at fitnesse.FitNesse.main(Unknown Source)

Press any key to continue . . .

Then you need to download and install version 1.5 or later of the JRE. Follow these steps: