Itunes Error 21 is the most typical error customers face while performing a restore on the iPhone. Tool Firmware Improve mode often called DFU mode, this mode allows you to restore your iDevice with an original iOS version or a custom iOS version.
To fix iTunes Error 21 in order to restore your iPhone/iPod touch, connect to your device into DFU mode first to get by following the instructions according to your device, The steps below will help getting into DFU mode in case you do not know how to:
How to Fix iTunes Error 21 While Restoring
- Connect your device to your PC or Mac via a USB cable and launch iTunes.
- Hold Home + Power button for 10 seconds.
- After 10 seconds release the power button off, but keep the Home button pressed until iTunes a little device in recovery mode you find there.
- Once your device into DFU mode, you see nothing on the screen, only a black image. (See above)
If you successfully performed these steps, iTunes will give you a message that a device was found in Recovery Mode and restore it. Now click on the SHIFT button + Restore in iTunes button, so that iTunes can refer to the iOS firmware to which you are restoring to. If you have followed these steps you should be able to fix iTunes Error 21 while restoring your iPhone / iPod touch. Now you have fixed iTunes error 21, and your iPhone can also be restored to an ipsw customized firmware.