mystery files

 From:  eric (ERICCLOUGH)
Hi ...
I have some dwg files of cars and such. They open fine as dwg files in various AutoCad clones.
I can open these files with Rhino (I am using Rhino 5) and then save them as 3dm files (either ver 4 or 5 - Rhino).
When I open these files with MoI there is nothing there ... the names of all the styles come through but no image ... nothing that I can find.
This is a mystery to me ... it has been my experience that Rhino 3dm files can be opened with MoI.
Any ideas?