Error 3002
- iTunes hasn't checked with Apple to see what the latest version is and so it is attempting to update to a firmware that is no longer signed.
- The update server may also be down - try again later.
- It can also happen if you attempt to perform an Update restore with a local TSS server, or the Cydia server. Click Restore instead.
- Error 3002 represents no update ramdisk when pressing Shift+Check for updates.
Error 3004
- There is no internet connection. Make sure you can connect to gs.apple.com on ports 80 and 443.
Error 3011
- Your hosts file may be malformed - remove any lines with gs.apple.com in it.
Error 3014
- Your hosts file may be malformed - iTunes didn't get a response from the TSS server. Make sure you can connect to gs.apple.com on ports 80 and 443, or make sure you can connect to TinyUmbrella/the Cydia server/