thank you for your answer. It seems, that I have not enough understanding how Forest Pack works. When I insert XRefs with the "Xref Objects" dialog of MAX (for example a car) into a scene, all the things I have loaded (geometry and material) will be updated when I open the scene next time if there are changes of the car. But if I load the car with Forest Pack, geometry is updated, but materials are not then there are changes of the car. I can instance the material and work on it inside the Forest Pack scene, but my wish was, that also changes of the material will be updated from the car.max. When I use the update button of the XRef Objects window nothing happens.
Only when I temporarily replace the Forest Pack item with another car and switch back to the first car the changes in the material are visible. For me it seems that Forest Pack doesnt handle inserted max-models in the same way as inserting as Xref Object does it. Is that right and where can I read more about it?