error 21
iphone 6 wont restore error 21
Check for hardware issues
For error 21..
Here's what to check:
- Make sure that you have the latest version of iTunes.
- Check for issues with third-party security software.
- Make sure that your USB cable, computer, and network are reliable. Then try twice more to restore your iPhone, iPad, or iPod.
- If you still see the error message, you can check for outdated or modified software or contact Apple Support.