I have a rather robust library of audiobooks that I had downloaded from Audible. I am able to transfer these books (entire library) onto my iPod. I just purchased an iPhone and noted that I am only able to transfer AAC files to my iPhone. The files that do not transfer are; 4 (MP3), per Format: in Summary, of the "Get Info" tab Shouldn't I be able to listen to these? I tried going to; Advanced>in iTunes>Create AAC Version, but get an error message. Any ideas?