I just had a curious incident involving my beloved AppleTV 2. I had run out of space for movies on my iMac and had hence bought an external harddrive and asked iTunes to move the Media-folder according to this:
http://www.macworld.com/article/157240/2011/01/howto_move_itunes.html

It worked fine and took 4 hours. During that time my AppleTV 2 hung and I tried to reset it a few times holding down the menu and down-arrow keys on the remote control. The screen saver with pictures from my iMac kept on going and apart from the flickering lights there was no contact from the remote control to the Apple TV.
Even after finishing the moving of files on the iMac, the Apple TV 2 remained uncontrollable with the remote control. I was able to push a movie from the iMac using AirPlay and saw it without any problems, but even after several restarts - hard, taking out the electric cord, as the remote control didn't seem to get through: when trying to restart, the lights were flickering correctly, but nothing happened after that, either the screen saver kept on going or the main screen was totally static, e.g. no commands from the remote control had any effect.
Then I decided to restore the software and (luckily) I had a micro-USB-cable at hand so I hooked it up to my MBP and used iTunes to restore everything. It seemed to work well, but gave me this error at the end:

appletv.jpg

Leading me to this page:http://www.apple.com/dk/support/iphone/updaterestore/?error=1602

That does not exist. I removed the /dk in the link and got to this page:http://support.apple.com/kb/TS1275 While doing so, the AppleTV rebooted and asked for input as if it was brand new. Ignoring the message worked and now I am back on track! I never followed up on the error, as everything seems to work fine.
Summary: When moving a iTunes Library that is connected to an AppleTV 2, first of all turn off sharing before letting iTunes move the library. This would most likely have saved my evening.