[How to]How to fix Error 20 iTunes While Restoring iOS 5 Custom Firmware on iPhone 4

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These errors typically occur when security software interferes with the restore and update process.


DOWNLOAD REQUIRED

Download Redsn0w 0.9.10b5 to create custom firmware.
Download iOS 5.0.1 firmware
Download iTunes 10.5.1

Step 1: Remove your SIM card (your micro or cut SIM card) and then connect your iPhone into your computer.

Step 2: Download the iOS 5 firmware for your iPhone 4 (from here)

Step 3: Launch the downloaded Redsn0w 0.9.9b8, click on the “Extras” from the main menu and click on the “Custom IPSW” option.

Step 4: Once done, under Extras option, click the “Pwned DFU” option to put your iPhone in DFU mode state.

Step 5: Then once in Pwned DFU mode, just launch iTunes 10.5 and then restore your iPhone.
Hold down the OPTION button then
Click on “Restore”, locate the custom IPSW file.

Step 6: Wait for iTunes to restore the custom iOS 5 firmware. Once completely restored, your jailbroken iOS device will automatically restart and

NOTES:  Since you don’t have a SIM card on your device iTunes will prompt you that your device is not activated.

Step 7: To activate, just simply disconnect your phone, then insert your SIM card and then connect it back to your computer.

Step 8: Activate your iPhone through iTunes or with SAM if you don’t the official SIM card of your device.