OK, I have 3 Apple TV's in the house. Two mk3's and a MK4 HD.
All of my audio and video files in one folder on one hard disk on my Mac.
On the MK 3 I can play any file on the computer on the MK4 HD I can only play purchased films if I use the 'app' from the main TV screen rather than the 'computers' icon. I can play them on the computer its self or on any of the other TVs.
I have restarted both the computer and the ATV with no avail.
I reset the ATV and started from scratch but the problem still persists.
Yes it works but its annoying having my library split and having to use two different methods.