Working on a box set. Had walls with wallpaper that I wanted to have a transparency so the light would shine through onto the set and the walls would glow a bit when lit from behind. Got that to work by turning off the cast shadows on the wall. Come back today and all my walls that have the wallpaper will not take light. The light will still go through the walls and they are still transparent but no light will illuminate them from the front or the back? Anyone?