A little searching goes a long way...
http://support.apple.com/kb/TS3694?viewlocale=en_US&locale=en_US
Errors 3000-3999 (3004, 3013, 3014, 3018, 3164, 3194, and so on): Error codes in the 3000 range generally mean that iTunes cannot contact the update server (gs.apple.com) on ports 80 or 443.
- Update to the latest version of iTunes.
- Verify the computer's date and time are accurate.
- Check that your security or firewall software is not interfering with ports 80 or 443, or with the server gs.apple.com.
- Follow Troubleshooting security software. Often, uninstalling third-party security software will resolve these errors.
- An entry in your hosts file may be redirecting requests to gs.apple.com (see "Unable to contact the iOS software update server gs.apple.com" above).
- Internet proxy settings can cause this issue. If you are using a proxy, try without using one.
- Test restoring while connected to a known-good network.