Hi, in the 9.1 version, there is message to a standard output at the beginning of G4Element::G4Element(const G4String& name, const G4String& symbol,G4double zeff, G4double aeff), which is printing out fNeff before it was actualy computed (and therefore the message is printing A = 0, which is misleading.....)
Thanks for the report - it is correct. The bug was already fixed. The fix is available with the 9.2beta version of Geant4 and will be inside new 9.2 release. best regards, Vladimir