I too was first but a passer-by.. in search of an elusive answer. After traveling to distant websites promising solutions and offering nothing but reboots and unneeded software.
But in the distance, on the second page of results from my 4th search query, MacRumors glistened over the click of 'Next page of Results'. The first recognizable URL in a sea of randoms. But could it be?? Could there be a true solution?? Or just more pages of disappointment? Worthless letters on the screen.. obviously fake Thank you post for a 'solution' that could have never worked...
But then I met your reply "NmeNotDisplayed"... You were my oasis in the desert. You were the voice of reason in a crowd of confusion. You determination bled through your response and pierced my suspicion's heart.
Sorry.. I too created an account because after half a day of searching, this was the only solution to work. I am now actually watching the update install when it was bombing out constantly after updating. Such a simple solution.
Again sorry for the dramatics... I needed something to do while the phone updates - finally!!
The solution is rather simple. Although there are many reasons for error 4000, including a bad cable - in this case there is a problem with updating via Windows 10's current version of iTunes and it is related to having a pass code and lock screen. Temporarily disable 1) your device pass code 2) screen autolock and try again. This solved my problem on 3 separate iOS devices. Once updated via Win10 iTunes, I simply turned my device pass codes and autolock back on.