These errors are typically resolved by performing one or more of the steps listed below:
- Perform USB isolation troubleshooting, including trying a different USB port directly on the computer. See the advanced steps below for USB troubleshooting.
- Put a USB 2.0 hub between the device and the computer.
- Try a different Dock Connector or Lightning Connector to USB cable.
- Eliminate third-party security software conflicts.
- There may be third-party software installed that modifies your default packet size in Windows by inserting one or more TcpWindowSize entries into your registry. An incorrectly set default packet size can cause this error. Contact the software manufacturer that installed the packet-size modification for assistance. Or, follow this article by Microsoft to reset the packet size back to the default for Windows: How to reset Internet Protocol (TCP/IP).
- Connect your computer directly to your Internet source, bypassing any routers, hubs, or switches. You may need to restart your computer and modem to get online.
- Try to restore from another known-good computer and network.
Error 2, 4 (or -4), 6, 1000, 9006
- Follow the steps to troubleshoot security software. Often, uninstalling third-party security software will resolve these errors.
- There may be third-party software that modifies your default packet size in Windows by inserting a TcpWindowSize entry into your registry. An incorrectly set default packet size can cause these errors. Contact the manufacturer of the software that installed the packet size modification for assistance or follow this article by Microsoft: How to reset Internet Protocol (TCP/IP).
- Verify that access to ports 80 and 443 are allowed on your network.
- Verify that communication to albert.apple.com or phobos.apple.com isn't blocked by a firewall or other Internet security setting.
- Discard the .ipsw file, open iTunes and attempt to download the update again. See the steps under "Advanced steps > Rename, move, or delete the iOS software file (.ipsw)" below for file locations.
- Restore your device while connected to a different network.
- Restore using a different computer.