Why does my apple tv keep saying to turn on home sharing on my computer when it is already on?

I can play all of my purchased movies and apps etc just fine on my appletv. My problem is when I go to play a movie from my itunes library it will not let me, telling me to make sure home sharing is on. It's turned on, on my computer, my appletv etc. I have restarted it, I have restored it, and I have reset it and it's a constant headache. No matter what I've done I can't get my itunes library to show up.