Material mismatching in render

[nirpolak1]

Hey, I'm having some troubles with rendering in autocad 2014 (student edition), as the final image shows parts that failed to render the material, mainly at backward areas. It's not a problem with the material itself, because I changed it to something completely different and the problem stayed.
Here's an exapmle, can you identify the problem?
Thanks!

[Anthonius]

What do you mean by "backwards" areas?  Are you referring to the grey-ish blocky things you're getting (some circled below)?

[nirpolak1]

Yes, it doesn't seem to apear on the front.

[Anthonius]

I think you and I are at odds with what we would call "back" and "front".  Those grey artifacts are on the "side" of the cathedral facing the "front" where the doors are - to me.

I don't suppose you could post the solid model dwg file?  Then I could open it and check.

One guess is that those particular pieces of glass have double solids on them.  Meaning two pieces of the same glass in the same place.

Could you perhaps make a couple of other renderings from different views so we could see those grey artifacts from a different angle?

[nirpolak1]

I meant fornt of the prespective, as everything closer to the camera seems fine, and from one point backward something went wrong. But nevermind that, I just thought it was related to the problem.

Duplicated solids were my guess too (I didn't made the model), so I'm fixing that now and will post tommorow if the problem continues. 

Thanks!