Bliz changed the model format ~1 year ago breaking all tools older than that.
Some tools have updated (such as
Retera's Model Studio or
RMS Twilac Edition #TwilacsTruly3D v05) others not so much.
I helped Ralle with the viewer to make viewing most models possible some month ago.
Edit: I didn't read where this was posted, so I'm not 100% sure if what I'm saying is any good. But I still think RMS is your best bet.