The message obtained if a user attaches more than one replica to a logical
volume is misleading:

G4SmartVoxelHeader::BuildNodes - PANIC! Daughter physical volume name =
grand_daughter_box_phys is entirely outside mother logical volume name =
sub_divided_tube_L

*** G4Exception: Aborting execution ***

This is because it is not properly trapped in G4SmartVoxelHeader constructor:

G4SmartVoxelHeader::G4SmartVoxelHeader(G4LogicalVolume* pVolume,
				       const G4int pSlice) :
                                       fminEquivalent(pSlice),
                                       fmaxEquivalent(pSlice)
{
    G4int nDaughters;
    G4VoxelLimits limits;	// Create `unlimited' limits object
    nDaughters=pVolume->GetNoDaughters();

// Determine whether daughter is replicated
    if (nDaughters!=1||!pVolume->GetDaughter(0)->IsReplicated())
	{
// Daughter not replicated => conventional voxel Build
// where each daughters extents are computed
	   BuildVoxels(pVolume);
	}
    else
	{
// Single replicated daughter
  	   BuildReplicaVoxels(pVolume);
	}
}

should have an extra clause, e.g.:

G4SmartVoxelHeader::G4SmartVoxelHeader(G4LogicalVolume* pVolume,
				       const G4int pSlice) :
                                       fminEquivalent(pSlice),
                                       fmaxEquivalent(pSlice)
{
    G4int nDaughters;
    G4VoxelLimits limits;	// Create `unlimited' limits object
    nDaughters=pVolume->GetNoDaughters();

// Determine whether daughter is replicated
    for (G4int i=0; i<nDaughters; i++)
      {
	if (pVolume->GetDaughter(i)->IsReplicated()) break;
      }
    if (i==nDaughters)
      {
// Daughters are not replicated => conventional voxel Build
// where each daughters extents are computed
	BuildVoxels(pVolume);
      }
    else if (nDaughters==1)
      {
// Single replicated daughter
	BuildReplicaVoxels(pVolume);
      }
    else
      {
	G4String message ("G4SmartVoxelHeader::G4SmartVoxelHeader: ");
	message += pVolume->GetName();
	message += " has more than one\n  daughter of which at least one, ";
	message += pVolume->GetDaughter(i)->GetName();
	message += ",\n  is a G4PVReplica - illegal.";
	G4Exception (message);
      }
}