skylight bug?

Hey,
Im trying to build an orc base but my skylight seems to leave black area's.
Does anyone know what the problem is?



Im working with 3dmax7.0.
My skylight settings are default.

Please anyone!?

i tryed "force 2 sided" but nothing changed.
Or is it just dodgy plane/box modeling?
I couldnt find any vertexes crossing eachother.

any help would be very apprisiated.

Greetz Xtrå