from the iphone wiki:Errors 20xx
Errors 2000-2009 (from Apple support): 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. If the issue persists, it may be related to conflicting security software.
Also make sure you have the latetst itunes