3dgal

Hello, I am actually a AutoCAD Viz 2008 user that is trying to import a file from my VectorWorks 10.5 using colleague. Hi is exporting to .dwg, but whenever I open his file they are coming over as 2D with no 3D info, just flat line drawings. I've had another colleague using AutoCAD 2000 try and open them and he is experiencing the same thing. Does anyone have any advice I can pass along to my Vectorworks friend so that I may successfully use his files?? Any help greatly appreciated.