I am also can't sync my ipad to itunes over WiFi even though i followed all the steps on Apple website. On my Ipad, it would say "sync will resume when CNU22881X1D is available." What's weird is that CNU2288X1D is classified as Books! I tried to reboot, and applied all the solutions in the previous posts, but nothing work! I just want to get my books from iTunes to my Ipad since my Ipad couldn't connect to Calibre content sever no matter what. Any suggestions??