'Create Advanced Iray Node' plane is not invisible in render?

HorusRa

I'm not sure if I'm doing something wrong, but I have a backdrop plane outside of a window and the lights from inside are casting shadows from the window pane frames on the background. I was told to stop this (in Iray) one can create a plane, place it in front of the other plane and in scripts, create an advanced iray node, and in the parameters tab enable 'enable iray matte.' It was said this plane will render invisible, but it is not. I turned the opacity off but that didn't help, plane was invisible of course but then the shadows continued to fall on the background plane. Any ideas?