I just went through a lot of noggin scratching over this very same issue. Let me offer this advice: There are three places in iTunes 10.6.3 that could affect an Apple TV's ability to access your library. First, make sure that you turn on Home Sharing under the Advanced menu in iTunes. Then, go to Preferences and under the Sharing tab, check the box that says "Share my library on my local network." Finally, under the Parental tab in Preferences, there is a checkbox to disable Shared Libraries (although if this has been checked, it will say so under the Sharing tab). I hope this helps.