What properties of a mesh can cause errors with collisions?

I have a character that gets around fine on many structures(meshes) for quite some time now but just recently, through process of elimination, I identified a mesh that was causing an "invalid position { NaN, NaN, NaN }" error after several seconds of being walked or driven on. I have no problem discarding the mesh because it isn't extremely complex but I am trying to figure out for future's sake what the issue is.

 

I solved it. Attaching a rigidbody to the mesh was the solution.