The file G4LowEnergyUtilities.cc has an include CLHEP/String/Strings.h which doesn't exist.
Seems to be one for you.
ls /afs/cern.ch/sw/geant4/dev/CLHEP/$G4SYSTEM/pro/include/CLHEP/String/ CmdArg.h CmdArg.icc CmdLine.h Strings.h Strings.icc Evidently, CLHEP/String/Strings.h does exist.