Poser does not like thin, long triangles. But you get some of those if you let Cinema triangulate your model. It's fine to use N-gons for modeling, but you have to cut them to tris and quads youself - and prevent long, thin triangles in the progress.

A ship in port is safe; but that is not what ships are built for.
Sail out to sea and do new things.
-"Amazing Grace" Hopper

Avatar image of me done by Chidori.