When editing a map we usually find a place to put a rock there and it looks really cool on that place but many times you end up with a black rock instead. i am not quite sure how can i fix this annoying problem but i think just moving the prop usually helps. though many times you can't do exactly that. Sometimes you can find the same problem applying to displacements for some reason and i dont know how to fix it. Does anybody know how can i fix these? if yes i would be really happy if i could get a response as soon is possible. thanks.