when i tried upgrade ios 6.1.1 to 6.1.3 via itunes, "An unknown error occurred (-1)" showed up about 75%percentage of the progress. cannot find any solution by searching on google.
BTW my PC‘s OS is Win 8 x64.
iPhone 4S, iOS 6.1.1
Check this support document here and search for Error -1 http://support.apple.com/kb/TS3694
Check this support document here and search for Error -1 http://support.apple.com/kb/TS3694
Thanks but not helpful on this issue.>.<~~
Well, if it is not the security software on the PC, then the next step is a hardware issue. You can try and restore again using the information in this support document http://support.apple.com/kb/HT1808. If that doesn't work, then you need to make an appointment at the Genius Bar to get the hardware checked.
In my case it was the USB cable who caused the problem! just replaced the cable and the iPhone restored just fine. If it isnt the cable, try to use another computer or mac and make sure you have the latest version of iTunes installed. Hope this works out for you if you still have the problem!
an unknown error occurred -1
