It might have happened that you are trying to restore your iPhone, or iPad through iTunes and suddenly iTunes error code 21 pops up on your display.  

Most of the time, this error code triggers when you’re attempting to connect your iOS device with iTunes. Once this issue occurs, then all the running programs start crashing.

So, if you encounter this error code then resolve it with the best process as soon as possible.

 What Causes iTunes Error Code 21?

Several factors are responsible for this error to hamper your task. To know them, take a look below.

• Incomplete installation of the iTunes application.
• Corrupt registry files can also be a valid reason for this error code.
• Virus attack can also be responsible.
• By chance you have deleted iTunes files, then sometimes this can lead to this error code.

Also, there are several reasons are responsible for this error code, however, the above mentioned are the most common.

How to Fix Error Code 21 on iTunes?

If you are unaware of how to fix Error Code 21, then try out the solutions that are described below.

Solution 1- Turn of the Antivirus

Your usable antivirus might do a great job, but sometimes this can restrict your iOS device to connect with iTunes.  In this condition, turning off the Antivirus can be a safe option for you.

However, executing this procedure is not a challenging task if you thoroughly follow the given points.

Step 1

At first, check whether the Anti-virus software has a firewall and also check if the iTunes is included in that list not.

Step 2

Apart from that, disable the Antivirus temporary. You can do it manually .

One thing you have to make sure that when this has been resolved, then you can again enable your Antivirus quickly.

Solution 2- Check the Host Files

In some rare cases, it is quite possible that the Host files block iTunes from connecting with the iOS device.

This solution needs a little bit of knowledge of how to access the server. Hence, if you focus on the following part, then this will surely make your task easier. 

We will describe the whole procedure here. Check it out.

For Mac Users:

If you are a Mac users, then,

1. At first, launch the application and after that, tap on the Utilities folder. Thereafter, you need to open the Terminal.
2. Now, type ‘sudo nano /private/etc/hosts’ command and hit the Enter button. 
3. Next, you should enter the Mac password and hit the Return key. Your entered terminal will now displayed on the host file. Scroll down till you see the line that contains this error code.
4. In case, the entry is not found, then there is no communication mismatch.
5. However, if the entry exists, then remove the whole command line that contains the entry.

Once you have deleted the command line, then try to complete the restoring procedure. 

For the Windows Users

If you use the Windows Operating System, then,

1. First, go to Run application. The simplest ways to open it is to press the Windows and R keys together.
2. Then, enter ‘C:\Windows\System32\drivers\etc\hosts’ within the Run box and hit the Enter key.
3. Your computer might ask you, how you would like to open the file, you have to find and choose the Notepad option.
4. Thereafter, an address list will appear on the screen. Search for any lines which contain the iTunes error code 21.
5. If you do not find any line, then there is no problem. 

However, if the line exists, then keep a backup and after that, delete the whole command line.

Finally, reboot your device and if you still encounter this error.

Solution 3- Check the Sensor Cable 

To apply this solution on your device, at first, you should open the iOS device. After that, remove the screw that holds the battery. 

Next, looking for a device cable and once you found it, then disconnect it. Again reconnect it after a few moments.

After that, reboot the iOS device and hope you can operate your machine without this error code. However, if not, then here we mentioned another solution to wipe out the flaw.

Solution 4-  Update iTunes

Sometimes, after updating iTunes to its updated version can help you in resolving the error. To apply this solution, first, you have to open iTunes.

After that, navigate to the Menu option. From there you should click on the Help option. In the next pop up window choose the ‘Check for Update’ option.

If an update is available, then it will show on the display. After that, click on the Apply button. 

Now, the updating process will be started. Wait for sometimes and once done, then reboot your system. Then, try to complete the pending task.

Solution 5- Use DFU Mode

In this solution, enter the iOS device into the DFU mode. If all the above solutions are unable to make iTunes error code 21 vanished, then only you can try this solution. Now,

How to Enter into the DFU Mode on (iPhone 6, iPod or iPad)? 

To enter into the DFU mode, at first, you have to turn off your iOS device. This can be done by simply holding down the power and home button together until the device is shut down.

After that, hold down the power button for 5 seconds. Next, hold down the home button also. Now, keep holding both buttons for 20 seconds. 

Thereafter, release the Power button. Keep pressing the home button for 7 to 8 sec. 

Once, you see that the LED screen is staying black without the Apple logo, that means DFU mode is on. Now, try to connect your iOS device with iTunes. 

Next, move to the Summary tab and tap on the Restore option. Then, follow the online instructions to complete the procedure.

How to Enter into the DFU Mode? ( iPhone 7 or iPhone 7 Plus )

Here are the ways that you can try to resolve your queries.

Way 1

Shut down your iPhone 7 or iPhone 7 plus device. After that, press and hold down the power button for 5 seconds.

Thereafter, press and hold down the Volume Down button together with the Power button.

Way 2

Keep pressing both the button for 10 seconds. Then, release the Power button but keeping the Volume down button for 5 sec.

After that, you have successfully entered in the DFU mode. Now, like the previous one, you should connect the iOS device with iTunes.

Furthermore, navigate to the Summary option and choose the Restore button. Next, follow the online instructions and complete the process.

Finally, the iTunes error code 21 will not appear on your screen anymore.