I just unplugged my ATV and closed itunes, then started all over again. tried that once before and it didn't work but the next time did. Hopefully it doesn't do this again!
I hope so too, since I have recently begun having intermittent problems with Home Sharing. Actually, the first problem I had was with Netflix just randomly quitting on me and giving me an error that the site was down. I confirmed that everything on Netflix's end was fine by streaming content via my computer and my PS3. I did a restore on the ATV2 and it has been working more or less okay since then, but on occasion I'll get a movie that will hang. I never have this problem on the PS3.
Yesterday the Home Sharing problem started. I went to the computer and Home Sharing was turned on and iTunes was running. I quit and restarted iTunes, but that didn't work. I had to turn Home Sharing off and then back on again, and that seemed to do the trick in getting my music to stream to my ATV2 again.
The other issue I have is that my ATV2 will only recognize some of my Aperture albums for the screen saver. No matter what I do, I can't get it to recognize a handful of albums I have.
I really like the second gen ATV, even more than the first gen I had, but these problems are starting to get annoying.