I have exactly the same issue - since yesterday. Until yesterday everything was working fine since months.
Yesterday I was listening to one of my purchased albums in iTunes Store on my ATV. Everything worked fine until the last song of the album. This song was suddenly interrupted, followed by the message that ATV can't connect to the iTunes store (No content found).
I also tried a lot of the hints above, including un- and replugging, new start, switching to a preview of a movie inbetween, etc... Sometimes it worked again for 1 or 2 songs but then the same issue occurs again.
Everything else works fine: I can watch movies, I can play music via AirPlay from iTunes running on my notebook > so it's definitely not a general network or wi-fi problem.
And it can't be the solution to replug, restart, connect via cable etc. everytime I want to listen to my purchased music on the iTunes store.
By the way: I thought about purchasing iTunes Match soon... but if this major annoying issue won't be fixed in general by Apple, I won't purchase any music content on iTunes anymore. If Apple is putting everything online or into a cloud, on web servers etc. they have to make sure that the users can access the content.