Chosen Solution
In the middle of restoring my iPhone 4S I have an unknown error (51). I have tried to restore in the DFU mode too.
Now I’m writing from that phone. The problem was resolved with the release of iOS 9.2. Perhaps the problem was specific to the firmware. If an error occurs when upgrading to iOS 9.2, just wait for the next version of the firmware. Unfortunately, while more anything I can not advise.
I have the same problem… please help us>!
