Apple has stopped signing iOS 10.1 and 10.1.1 on Tuesday in a move that's sure to choke the jailbreak community a little bit further. It's typical of Apple to follow this kind of behavior after a new firmware release, so it's not surprising this would happen as iOS 10.2 was released just over a week ago.
With the firmware no longer being signed, downgrades to iOS 10.1.1 are currently no longer possible, so if you've upgraded to iOS 10.2 recently or need to do a fresh restore of iOS 10.1.1 in iTunes, then you're out of luck.