I have got it working and the only thing I can think, is that you may have missed a step in the installation:
Then place the binary javacc-7.0.9.jar in a new target/ folder, and rename to javacc.jar.
If you did this then make sure that the
target
folder is in the correct place, which is in the
javacc
directory at the same level as the
scripts
directory.
No doubt they could have made the installation process easier.