Ya i had the same problem!! I tried almost a hundred times. I didnt rlly need the jb anymore so i reset the ipad, erased all contents and settings, erased all jb apps, erased cydia (deleting the cydia installer package), and the. Rebooted but it still wont let me update!! Its techniacally un jailbroken, right?! No cydia, but for some reason my music app has no icon and is still unified with videos but i also have the videos app. Confused about that...
Wutevr...my windows crapyop broke a cuple weeks ago so im waiting to get the new mac this april so im computerless till then. Hopefully my brothers computr doesnt lag itself to death before i update...