Hi Tolek,
The problem you are having sounds like one I saw last July where somehow the multi/sub-object material got corrupt, and for some reason typing names for each material ID fixed the problem. That post can be found
here, complete with pictures.
If that doesn't work, I'd like you to follow the directions in
this post so we can determine if it is a problem with Vizard reading the files or a problem with Max exporting the files.