You may have to recompile G4Java. It consists of a Java part and a native C++ part. The NAR Plugin handles the compilation of the native part and its native dependencies (geant and clhep).

Get the code and build

To download G4Java type

svn co svn://svn.freehep.org/svn/sandbox/G4Java

and compile it by typing


This may take quite some time the first time as the correct geant and clhep libraries need to be downloaded and unpacked.