This article is useless, since songs aren't always the problem. But of course iTunes won't TELL YOU what the problem is.
So currently my setup is useless, because iTunes refuses to sync my phone with a new computer because some items are "unauthorized." Yet after I authorize the computer, iTunes whines that the computer is already authorized.
This article is garbage, because it assumes that songs are the problem. I don't have any purchased songs on my phone. What about APPLICATIONS? You can't find out what account was used to purchase them, because they aren't shown in the list of apps in iTunes (yet iTunes says they're there, even shown screens full of them).
What are we now, seven years into the iPhone, and we're still limping along trying to manage the contents of a handheld Unix computer with a JUKEBOX APPLICATION?
Pathetic.