Another inverted normal question

So I'm trying to upload a skeleton that is made up of individual bones intersecting each other (basically so I can put it in different poses) and I know that meshes can intersect each other with no problem. The problem is that I have already uploaded the body without the head and it worked fine, but when I attached the head, I get the inverted normals error. So I then uploaded the body again and the head again as separate files and they worked. I just don't understand why it doesn't work when the parts are together. I ran an STL check and got no errors, I'm really confused by this, maybe there is something I am overlooking. If anyone has any suggestions it would be greatly appreciated, I really want to get this printed.
I'm using 3ds max
Here are the stl files if you need them

Hi Rbot,

I have looked at your model and there were about 7000 intersecting triangles in your model causing the model to fail. I have cleaned up your model.

Cheers!

Robert

Hi Robert,
Thank you for the help, but I tried to upload the model and I'm still getting the same error message. I can do a simple work around and just print them separately, but I'm really interested in learning how to avoid this problem all together for future projects. I'm assuming if the model was one continuous mesh (non intersecting meshes ) with no inverted normals, broken edges, unconnected verts, or non manifold areas I could avoid this problem altogether.

Thank you

Hi Rbot,

Hmmm... I missed something. The model is three-manifold instead of two-manifold. That needs a manual fix and since I am not a 3D designer I am a bit at a loss here. Normally I verify any fix but this time I was a bit in hurry.

I understand your question that you would like to learn. Attached is a picture showing all intersecting triangles.

Cheers!

Robert

Hi Robert,
Awesome, the picture helped out a bunch, I'll just go ahead and work on making it all one solid mesh and that should fix the problem.
Thanks again, I appreciate the help.