I am trying to sync my iphone with my itunes library, but it says it is synced with another library. I don't have any songs on my iPhone, but it wants to "erase my iPhone" does that just mean the music, or is it going to erase my apps and stuff too?
That is probably what is wrong here. I would just back up right now and then try clicking the Sync after the back up and see if it says the same thing. Still I would erase yet because there may be other solutions that I don't know about.