Reading in TGeo objects from file, using geomRootToGeant4 and getting "No elements defined"

Hi VMCers,

I'm trying to put together a VMC application by following the Ex06 that comes with geant4_vmc. I'm having trouble using the "geomRootToGeant4" option to TG4RunConfiguration. If I use "geomRoot" then the initialization seems to go okay. The specific error I get is:

Converting Root geometry to Geant4 via VGM ...

    Geant4GM::Material::Material:
    No elements defined.*** Error: Aborting execution ***

There are two things I do differently from Ex06 that may be at fault. Please let me know if either is "bad".

First, I'm building the geometry separate from my VMC app. I populate a TGeoManager and then call it's Export() method to save itself to a ROOT file. In the VMC app I then call Import() on the file. I've browsed this file and plain-ROOT seems to be happy with it. My VMC app's ConstructGeometry() method is then mostly empty except for the call to:

    gMC->SetRootGeometry();

Second, when I create the geometry, instead of creating TGeoElement objects via "new" I get them by calling TGeoElementTable::FindElement() on the element table which I get from the TGeoManager.

Are there any hints of wrong doing from this information?

-Brett.