I had a problem today where none of our Apple devices would work on the Apple related services. Our AppleTV had no access to the Internet and could see our server, but wouldn't actually play anything. And our iOS devices couldn't use Home Sharing. It could see the server, but would get an "You do not have permission to access this content". And my Mac could not access the Apple website, nor could iTunes access the store. Also Netflix didn't work from any of our iOS devices. After some hair pulling and restoring of the AppleTV, I finally discovered that AT&T DNS service was to blame. I switched everything over to Google DNS (184.108.40.206) and suddenly everything worked again. What caught me off guard was that even when playing local content from a server, AppleTV still has to go out to the Internet to validate the iTunes accounts for Home Sharing. I was shocked to only see 2 icons on the screen.