this might help
I'm a PC user and over the past few days, my AppleTV has been dropping out of itunes for no what seemed to be no apparent reason. I loaded iTunes on different PCs, entered the access code in iTunes and every time, the AppleTV would drop out after about 5 minutes.
I was reading a little about WEP and other security settings and I remember that before i upgraded to a different access point, i was only using MAC address filtering and nothing else. When i installed the new access point, I didn't use MAC filtering and only WEP.
SOLUTION:
Something with the encryption i was using because i turned the encryption off and turned on MAC filtering. I need some type of security even though MAC filtering isn't that great. Anyway, it works like a charm. Apparently WEP or WPA doesn't work well with the latest versions of appleTV and/or iTunes.
I hope this helps.