ITunes won't let me buy a song?

I'm trying to buy a song from iTunes called Black Sheep by The Evil Exes from Scott Pilgrim vs the World. But whenever I click on it it says "could not purchase there is a problem with iTunes please try again later." But then I scrolled down and iTunes allowed me to buy 2 other songs from the same Soundtrack. Why won't iTunes let me buy that one song and how do I get it?