Geometry import issue

Hi,

I am having trouble importing a geometry from 3dsmax to Unreal. It is a box with an arc hole for the window. The problem is that when I import it into Unreal the faces are not shown, like when you have flip normals, but the normals in this geometry are ok. Do you have any idea what the problem could be?
I have attached an images where you will see what I am talking about.
Thanks.