I'm trying to create a ringtone in itunes. The audio file I have is not something I downloaded from the itunes store. When I choose Store>Create Ringtone, I get an error message that says "A ringtone cannot be created from the song 'NCIS Theme Music'. You can create iPhone ringtones only from songs purchased from the iTunes Store." My question is why is that? Why can't I create a ringtone from a song downloaded outside the itunes store?