Wukas your problems with the light maps is that you have multiple faces with more than 4 vertex,what i mean is that you have faces formed by 5/7/10 vertex, in case you did not know when you export a design to the format". Rs/elu/fbx" 3dstudio divides the faces formed by 4 vertex to 2 sides of 3 vertices (It separate a square face to 2 triangle faces), these are called assents which the mwe uses to calculate and generate the light mapping.
if your getting black faces when light mapping it means that you have a faces formed by 5/7/10 vertex so the 3dmax ain't able to convert it into assents witch gives you collision/light mapping problems it's ok to form faces from: 3/4/6/8 vertex because the 3dmax is able to convert it into assent.
You may check this by de-activating the option: edge only, if the 3dmax in unable to separate the faces into triangles it means that part gonna give you troubles either in collision or light mapping
example: