It looks liek you may have doublesided polys there. Try adding a tiny amount of displacement to the back wall, like 0,01  with a noise node - that's too small to be seen but should fix the problem if it is caused by what I think it is :)
Nice transporter room btw ^_^

FREEBIES! | My Gallery | My Store | My FB | Tumblr |
You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.