also check settings > music and make sure "use cellular" is enabled (something like that, I don't have it in front of me). If that is off but "show all" is on and you are on a cellular network vs. wifi you will see all your music but not be able to play it.
What if we are having this problem but don't want to use iTunes match and also don't want to allow anything over cellular because we don't have much data?
I have tons of greyed out songs but they are all mp3s that I imported into itunes after either ripping a cd or buying from Amazon digitally. This problem is super annoying. I have a playlist with 750 songs on it and only about 1/3 of them are actually playable.