“When I connect my iPhone with iTunes to do the update, it told me that I need to restore the iPhone. It will get all the way to ‘preparing iPhone for restore’ then will say, ‘The iPhone could not be restored. An unknown error occurred(21).” Does anyone know what else I could do to fix it? Please help.”
Most of iPhone users complained that iTunes 21 happens from time to time when they are trying to restore or update iPhone when using iTunes. It's like a whack-a-mole, you keep trying to restore, but that infernal iPhone Error 21 comes again. Generally this error is a result of some security software package interfering with the restore, and it usually has an easy fix. In this article, we will show some methods that are most likely going to work and fix iTunes error 21 when restore or update your device.
Reasons of iTunes Error 21
-Corrupt download or incomplete installation of iTunes software.
-Corruption in Windows registry from a recent iTunes-related software change (install or uninstall).
-Virus or malware infection that has corrupted Windows system files or iTunes-related program files.
-Another program maliciously or mistakenly deleted iTunes-related files.
Runtime Errors such as “Error 21” can be caused by a variety of factors, so it is important that you troubleshoot each of the possible causes to prevent it from recurring.
How to Solve iTunes/iPhone 21 Error While Restoring iPhone
Solution 1: Restart iTunes to Fix iTunes Error 21
If the iPhone error 21 is a temporary glitch, restart iTunes should take care of it. iTunes error 21 is a result of the iTunes being blocked. Sometimes simply restarting the iTunes, then starting the restore again can prove enough to fix iTunes Error 21.
Solution 2: Fix iTunes Error 21 by Updating iTunes
Updates on all Apple products can be imperative as they help fix bugs and whatnot. So if you have been holding out on updating iPhone because you have a slow net, or because your phone is jailbroken, or whatever reason you might have, now is the time to update it. Get the latest version of iTunes and you might be able to fix iTunes Error 21.
How to fix iTunes error 21
Open up 'iTunes.'
Go to Menu > Help.
Select 'Check for Updates.
Solution 3: Turn off Anti-Virus to Fix iPhone Error 21
A lot of times the proper functionality of some vital programs may be hampered by the anti-virus as they might be corrupted or be threats. In that case, turning off the Anti-Virus helps access those programs regardless and maybe update your device.
Solution 4: Remove Unnecessary USB Devices
You could try and fix iPhone Error 21 by removing all unnecessary external devices from the computer as they may have programs that are getting in the way of a proper restore and bring-ing up iPhone Error 21.
Solution 5: Check Sensor Cable
This method sounds either complicated or risky. However, it's not, not unless you do it exactly as it's supposed to be done. It's sorta' like defusing a bomb, cut the wrong wire and your device goes boom! Well, not literally, but you get the picture. However, if you do it right, you might be able to fix iPhone Error 21. All you have to do is open the device, confiscate the screw which connects the battery. Disconnect the device cable and put it back together.
Solution 6: Fix iTunes Error 21 via Recovery Mode
Step 1. Put your device into DFU Mode.
1. Hold the power button down for 3 seconds.
2. Hold the power and the home button down for 15 seconds.
3. Release the power button while still holding down the home button for 10 seconds more.
4. You'll be asked to "connect to iTunes screen."
Step 2. Connect to iTunes.
Plug your iPhone into your computer, and access iTunes.
Step 3. Restore iTunes.
Open 'Summary' tab in iTunes, then click 'Restore.'
After Restore, your device is going to Restart.
When asked to "Slide to set up," simply follow the Setup.