I get running geant4.3.2 G4VDecayChannel::FillDaughters 0:rho0 is not defined !! while G4RhoZero does not exists since geant4.2.0
The class G4RhoZero does not exist because "rho0" particle is not stable particle. Now rho0 is defined as a G4ExcitedMeson object. So, you should invoke G4ShortLivedConstrcutor::ConstructParticle() method.