Hey guys.. So I had this problem last night (Sept 6) out of nowhere with my Apple TV 2 and found this thread. I thought I would put my thoughts down of frustration and success..
Internet was working fine. Macbook pro worked fine on my network. iMac worked fine. iPhone worked fine. Apple TV 2 just would not accept my iTunes password even though it was working on all my other devices. My homeshare password is the same as my iTunes account so no problem there.
I checked for an Apple TV 2 software update but was updated.
I figured out the problem was this: Apple TV 2 somehow got kicked off the network and lost the current date and time. When I unplugged the Apple TV 2 from the power (not just turned it off) I let it restart. It took about 10-15 minutes to get the date and time, but after that my iTunes account password worked!
Try these steps if you are having this problem.
1) Disable and re-enable homesharing from the computer you are trying to connect with. (this works most of the time)
2) UNPLUG Apple TV 2 from the power for about 30 seconds and let it restart again.
3) Allow it to set the date and time (make sure to set your date and time settings to "automatic" before you do this) It might take it awhile to set the date and time. That's OK. Make sure it does this.
4) Re-enter your iTunes account name (a secret I found is that there is a "recent" tab on the top right of the keypad so you don't have to keep RE-typing it)
5) Re-enter your iTunes password.
And you should be in business because it knows the date and time.
It was a frustrating evening, but with a few steps and patience, I was up and running again.
andrew