During Geant 4.8.1.p01 installation in Scientific Linux 4 using the latest CLHEP 1.9.3.0 library, the build process terminates with errors (see attached g4make.log file). Hence the installation cannot be carried out. Typical errors look like: include/G4MCTGenParticle.hh:37: error: `HepMC' has not been declared include/G4MCTEvent.hh:45: error: `HepMC' has not been declared Reinstalling everything, but with CLHEP 1.9.2.2 instead of 1.9.3.0, solved the problem.
CLHEP-1.9.3.0 (and 2.0.3.0) are just recent and therefore NOT supported by any Geant4 version ! Please, read the release notes of Geant4 8.1 to see what is the right version of CLHEP supported.