8 Ways to Repair iTunes Error 21 or iPhone Error 21 [2024]

By Nathan E. Malpass, Last updated: March 1, 2024

The iPhone "iPhone" could not be restored. An unknown error occurred(21). How to fix this iTunes Error 21 (iPhone Error 21)?

When using your iPhone or iOS device you may have encountered bothersome problems which may have soured your day. This can range from accidental physical damage, a software issue, or a hardware malfunction.

As with all devices, no matter who the manufacturer is, unfortunate errors may occur out of the blue. Apple iOS devices are no exception and are not exactly flawless in their design. However, all the blame cannot be placed on the manufacturer.

The mishandling of an iOS device by the consumer will also potentially bring out problems. It is, therefore, important to always take care of your gadgets.With that said, today we will cover a software error that may occur in your iOS device through being mishandled or through pure software malfunctions.

This common error is the iTunes Error 21.Let us look deeper into what this error contains and discover ways on how we can fix it.

Part 1: What Is iPhone Error 21 on iTunes?Part 2: What Causes Error 21 Happen When Using iTunes? Part 3: 7 Common Solutions to Fix iTunes Error 21 Part 4: The Easiest and Most Efficient Solution to Solve iPhone Error 21 Part 5: Watch Video Guide to Fix iTunes Error 21

Before We Repair iTunes Error 21:

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If you don't feel like help from third-party software and want to fix it on your own, we have also collected some common solutions below.

Part 1: What Is iPhone Error 21 on iTunes?

Error 21 is an error which you may encounter when you are attempting to restore or update an iOS device such as the iPhone, iPad or iPod. This is pinged and pops up when you have connected your iOS device to iTunes.

To be a bit more detailed, iTunes is in the process of checking the authenticity of the firmware file (extension ending with .IPSW) but ‘something’ caused it to go awry.

Symptoms of Error 21 That Have Been Recognized

1. The “iTunes Error 21” notification box is displayed.

2. After its appearance, the program crashes.Your Mac or PC may crash altogether.

3. Your Mac or PC may perform slower and be unresponsive or lags during mouse and keyboard inputs.

4. Your Mac or PC experience constant short freezes unexpectedly.

*Take note of any of these symptoms and EXACTLY when they occur.
*Your Mac or Windows PC may or may not be subject to these symptoms but always be aware and ready to use the methods that will be presented later.

fix-iphone-error

Part 2: What Causes Error 21 Happen When Using iTunes?

The most common reason for iTunes Error 21 is that your iTunes is trying to download the restore files (.ipsw) but is unfortunately being blocked from authentication. This may be due to a hardware error, or maybe there is a communication failure between your device and the servers. some several possible reasons why iTunes Error 21 occurs are as follow:

A corrupted download or incomplete installation of the iTunes software had occurred.
A corrupted binary in the Windows registry which is related to iTunes.
A virus or malware has corrupted Windows or iTunes files.
iTunes files have been deleted, either intentionally or unintentionally by a program.

While there may be more reasons as to why the error appears, the above mentioned are the most common.

The question probably posed now is, “What do I do?”
Don’t panic, just relax and read on as we will now show you the several common ways on how to fix this issue.

itunes-error

Part 3: 7 Common Solutions to Fix iTunes Error 21

Now that we are on to fixing the error, please note that there are numerous ways to troubleshoot this problem. As previously mentioned, there are several causes to why the error appears, so do not be discouraged if one method does not work, simply try the others! Here are the steps to fix the iPhone error 21.

Restart iTunes by updating iTunes
Update iTunes to Repair iPhone Error 21
Turning Off or Adjusting Your Anti-Virus
Checking the Host File
Unplugging Any Unnecessary USB Devices
Checking the Sensor Cable
Using DFU Mode to Fix iTunes Error 21

Method 1: Restart iTunes by updating iTunes

At times, the fix required can be as simple as this. Due to corrupted files which may have stemmed from computer lag or if the connection between your iOS device and computer was interrupted, a simple restart is perhaps needed.

Go ahead disconnect your iOS device, shut down your iTunes and restart it. Reconnect your iOS device to your Mac or Windows PC and attempt to update or restore again.

If that worked, then it may have been a simple computer fault. If not, please read on to the next method.

itunes

Method 2: Update iTunes to Repair iPhone Error 21

Sometimes the error occurs due to iTunes being way outdated. If Method 1 didn’t work then this would be the next logical step.

Simply have iTunes open and go to the ‘Help’ tab. From there click on ‘Check for Updates’.
Another way is to uninstall iTunes and search online for the latest version to download.

If this still did not work - continue on.

itunes-update-iphone

Method 3: Turning Off or Adjusting Your Anti-Virus

While turning off your anti-virus is a risk, it may be what is needed to get the pesky error to disappear. Anti-Virus programs do a good job, but sometimes they tend to block programs despite them being flagged as safe.

Attempt to do the following:

Check if your Anti-Virus program has a firewall and see if iTunes is exempted from the list. You may also need to check if Windows Firewall has it exempted if you are using a Windows PC. If either one or both does not have it included, add iTunes now on the list(s).
If that did not work, then you may turn off your Anti-Virus temporarily, either manually or with a timer. Make sure it turns back on after trying to update or restore.

Hopefully, through having to take these risks, the error should be long gone.

anti-virus

Method 4: Checking the Host File

In some cases, it may be that your host file is blocking iTunes from communicating with Apple’s server in order to update.

This method requires a bit more effort on your part as you would need some knowledge in accessing servers. Also, this may or may not be the solution, but if you are willing to go through with it, we will provide you the details here.

If you prefer an easier way to fix iTunes Error 21 quickly, you can always try iOS - System Recovery to repair your iPhone. It helps automatically detect the error and fix it in minutes.

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If you want to try your best to check the host file, here are the steps:

For Mac Users

1. Launch ‘Applications’ and click on the ‘Utilities’ folder.

2.Open ‘Terminal’

3. Type the command: sudo nano /private/etc/hosts

*Note that there is a space between nano and the ‘/’.

4. If prompted to input your password, use your Mac password and press the ‘Return’ key.

5. The terminal that you have entered will now display the host files related to what you have typed. Scroll down until you see an entry that contains.

If this entry isn’t found then there is no communication blockage.

If the entry does exist, delete the entire command line that contains.

6. If you had to delete the line, check with iTunes if the error still occurs by updating or restoring.

For Windows Users

1. Go to ‘Run’. The easiest way is to press the Windows Key + R.

2.Type in: C:\Windows\System32\drivers\etc\hosts

3. Your computer may ask you on how you would like to open the file, find and select ‘Notepad’.

4. You should now get a list with hashtags and addresses.

5. Look through to find any lines that contain.

If this entry isn’t found then there is no communication blockage.

If the entry does exist, BACK UP by saving a copy then delete the entire command line that contains.6. If you had to delete the line, check with iTunes if the error still occurs by updating or restoring.

If iTunes finally started to behave after this process, then you are all set. However if not, you know the drill - continue on.

Method 5: Unplugging Any Unnecessary USB Devices

Sometimes a computer may be confused if so many USB devices are plugged into the ports. Go ahead and unplug everything else except your iOS device and check to see if it helped.

fix-iphone-error-usb

Method 6: Checking the Sensor Cable

Moving back to something more difficult, if not the most difficult method on this list, it may be the fix required if everything else failed.

If you don’t know how to tinker with devices we suggest to leave this to someone who can.

If you do know, however, here is what you need to do.

*Prepare hardware tweezers or something that can firmly grab small items.

1. Open your iOS device.

2. Remove the screw which holds the battery in place.

3. Look for a device cable and disconnect it then reconnect it.

4. Done!

While it may not be as hard as it seemed, make sure that everything was perfectly done in reverse.
Hopefully, this had done its job, but once again if not... Then prepare for the second to the last method.

Method 7: Using DFU Mode to Fix iTunes Error 21

In this method, the iPhone would need to enter DFU Mode. This mode is the deepest type of recovery available and should be able to make Error 21 vanish forever. Only try this method if all other options have ended up not producing results.

Preparation

Make sure that you have successfully backed up all your data. Doing this via iCloud would be optimal.
It is a good practice to charge your iOS device to at least more than 50% battery life. This ensures that the process won’t be interrupted - important if your area suffers from power outages. During these times a laptop may be needed as a desktop will completely be unusable.
Know what all the buttons do - Home Button, Power Button (a.k.a Sleep & Wake Button). For an iPhone 7 or 7 Plus, the Home Button is no longer relevant. In this case, the Volume Down button is used in its stead.
Have your iOS device compatible USB cable ready.
Count your seconds properly or use a timer. This is very important.

Precautions

Completing recovery with the DFU Mode results in loss of data, it is, therefore, imperative to have your data backed up so it can be easily retrieved later.
Make sure no damages to any components are reported, especially with water - this may abruptly cause ‘premature completions’ or none at all. Please note that while the iPhone 7 and 7 Plus are waterproof, any open cracks will still allow water to do damage.

If you tried Method 6, make sure you did not damage any components.

enter dfu mode

How to Enter DFU Mode (iPhone 6, iPod or iPad)

Shut off your iOS device. (Hold the Power Button until a red slider appears then slide to the right) (This can also be done by holding both the Power Button and Home Button until it turns off).
Hold down the Power Button for 3 seconds.
CRUCIAL STEP: While still holding down the Power Button, press and hold the Home Button.
Hold both buttons for exactly 10 seconds and release ONLY the Power Button.
Keep holding on to the Home Button for 5 seconds.
Once you noticed your screen is staying black without seeing the Apple logo, you have successfully entered DFU Mode.
Connect your iOS device to your computer and have iTunes ready.
Go to the ‘Summary’ tab and select ‘Restore’.
Your iOS device will begin to restart.
Follow the steps once it reboots and confirms if the error still exists.

On your Mac or Windows computer, a screen should pop up indicating that it has detected a device in DFU Mode. (It may say “recovery mode” - but as long as the screen is black you are officially in DFU Mode).

*This process may take a few tries to succeed. Timing is important so proper counting or a timer is recommended.

How to Enter DFU Mode (iPhone 7, iPhone 7 Plus)

Turn off your iPhone 7 or 7 Plus (Hold the Power Button until a red slider appears then slide to the right).
Press and hold the Power Button for 3 seconds (It is on the right side of this model).
Press and hold the Volume Down button (found on the left side of the device) simultaneously with the Power Button.
CRUCIAL STEP: Proceed to hold both buttons for exactly 10 seconds.
Release the Power button but continue to hold down the Volume Down button for 5 seconds.
Once you have noticed the screen stays completely black, you have entered DFU Mode.
Connect your iOS device to your computer and have iTunes ready.
Go to the ‘Summary’ tab and select ‘Restore’.
Your iOS device will begin to restart.
Follow the steps once it reboots and confirms if the error still exists.

How to Enter DFU Mode (iPhone 8 and Later Models)

Connect the iPhone 8 or later models to a computer using a USB cable.
Press the Volume Up button quickly.
Press the Volume Down button quickly.
Hold down the Side button until the screen goes black, then continue holding both the Side button and the Volume Down button.
After about 5 seconds, release the Side button while keeping the Volume Down button held down.

If iTunes is open, it will alert you that a device has been detected in recovery mode. If your device displays a screen prompting you to connect to iTunes, try these steps again.

Now that you have gone through the whole process, this should have fixed the issue.

While DFU Mode is the utmost final option available wouldn’t it be better if there was an easier, hassle-free option? The answer is YES, there is such option you can take advantage of!

Part 4: The Easiest and Most Efficient Solution to Solve iPhone Error 21

This is where FoneDog - iOS System Recovery becomes a total no-brainer to use.

Here are the steps for eradicating iTunes Error 21 forever:

1. Download, install and launch FoneDog toolkit. Once you have launched the program, verify that our easy-to-use interface is visible on your screen.

2. Plug in your iOS device to the computer via USB cable. Confirm that FoneDog toolkit was able to detect your device.

3. In the main menu, click on ‘iOS System Recovery’. You will now notice several other options such as ‘iOS Data Backup & Restore’, “iOS Data Recovery” and the like. These are for anything else you need repairs for.

4. Click ‘Start’.

5. Your iOS device will once again be automatically detected. Its firmware can be updated by clicking on ‘Repair’.

6. Recovery will begin immediately. As you may have noticed, all errors are gone as it undergoes restoration!

7. Finished!

start

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Part 5: Watch Video Guide to Fix iTunes Error 21

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