Softshadows Xfile light artifact in corner


firstly thanks for this shader!!
i am trying to rebuild help file, i have imported there mine Xfile, but i am getting strange error light coming in through front side (corner) and doing strange light artifact on opposite site corner as the light is coming.

have i export wrongly Xfile? i am using KwXport.
in zip there are two variations one is one side wall second has thick walls.


SoftShadowsXfile.ZIP (8.5 kB)