Why aren't some of my songs transferring to my new iPhone? I purchased a new iPhone a couple days ago. During the setup process, I restored from a backup of my old iPhone, from about two weeks ago (the old iPhone was stolen, so the backup was a bit old). When I restored, I got a warning that 21 items could not be synced, and to check iTunes for more details. iTunes did not give me any warnings or information at all.

I noticed that the 21 songs are all songs I had previously purchased from the iTunes Music Store. They are not on the iPhone; in the iPhone music list view (in iTunes), they all have a sync icon next to them:



I can't seem to get them transferred to my iPhone. I tried removing all the music from the iPhone and resyncing, but they still were not transferred. I then reauthorized all my computers, and re-authorized my computer, but the songs would still not sync.

What's wrong? Is there a way to sync these previous purchases to my iPhone? I should note that this is not happening with all of my songs; some purchased songs were transferred successfully.
After trying a series of troubleshooting moves, including restoring my iPhone from an iCloud backup, the only thing that worked was restoring my iPhone from an iTunes backup, as described in this article.