what causes error 2001
When I tried to restore and update an iPhone 4 the process stopped with a message: "The iPhone cannot be restored. An unknown error (code 2001)". Who KNOWS what the error is?
iPhone 4, iOS 6
Error 2000-2009 (2001, 2002, 2005, 2006, 2009, and so on)
If you experience this issue on a Mac, disconnect third-party devices, hubs, spare cables, displays, reset the SMC, and then try to restore. If you are using a Windows computer, remove all USB devices and spare cables other than your keyboard, mouse, and the device, restart the computer, and try to restore. If that does not resolve the issue, try the USB issue-resolution steps and articles listed for Error 1604 above. If the issue persists, it may be related to conflicting security software. If the errors persist on another computer and known-good USB cable, the device may need service.