Q: How to fix error 2 iphone 4

Check your security software

Related errors: 2, 4, 6, 9, 1000, 1611, 9006. Sometimes security software can prevent your device from communicating with either the Apple update server or with your device.

Check your security software and settings to make sure that they aren't preventing a connection to the Apple servers.

I'm having the same problem. My itunes window jumps while the process is almost done (apple icon with status bar ongoing) and shows me the same message. And I've already tried to turn off my firewall off, tried to enter the DFU mode... Nothing really works.