Error 20000-20008: This error may indicate that you have a USB communication failure due to a damaged USB 30-pin Dock Connector cable, out-of-date USB device drivers or firmware, or that other USB devices connected to your computer are interfering with iTunes communicating to the iOS device. Try restarting the PC and testing again with a different USB port. If you are using a custom Windows Theme Pack, revert to the default theme pack, restart, and try to back up and restore.
Source [Apple]
