For some reason, when I check the box to "Manually manage music and videos" in iTunes, it tells me that my iPhone is synced with another iTunes library and I have to erase the iPhone to sync it with this one. The problem is, I've only ever used it on this computer! I added 30 GB of music to it two days ago, and then deleted the 30 GB from my iTunes library but not the iPhone; would that have anything to do with it? Any help would be greatly appreciated!