I'm trying to get the new Kenny Chesney song, same prob.
Best I've done is go to 4G on my iPhone, no WiFi, bought it there (it worked) but now I can't get it to transfer over to my MacBook. So annoying, there are actually a lot of questions about it in the Help section of iTunes. No real answers though. A few people have had luck using different WiFi set ups other than their own, like finding a hot spot.