Also what I did to work around this:
[*] Create a virtual machine and install windows on it
[*] Only install what you really need (like a Browser and Dropbox)
[*] Install newest versions of GM2 onPC and GM2 3D
[*] Import the showfile you've been working on
[*] import 3D model
[*] save it and open up the showfile back in your regular setup
Worked for me.
I'm pretty sure that the issues we're all having are coming from multiple/old version not getting along with newer versions of GM2 onPc/3D. So I'm guessing that's why this approach works. Also probably never hurts to work on a fresh windows setup ;)
Hope that helps :)