571      iPhone_iPad_Mac_apple

Error 21 while trying to  update/restore

I get an "Unknown error occurred. (21) when trying to perform the iOS 5 update and restore.

The iPad is left in the restore state and cannot be used.

Unplug unit from computer, Shut of iPad completely, Hold home button and while holding plug into itunes, it will say connect to itunes then go to device and click restore

Upon connection I get "iTunes has detected an iPad in recovery mode and must be restored".  However I get the same message.  "The iPad cannot be restored. An unknown error occurred (21)."

Thanks for the tip, however it did not make any difference.  Sincerely Bruno.

Try disabling Security Software

BACKGROUND:  I purchased two brand-new iPads and a new iPhone today.  I udpated the iPhone and one iPad; on the other iPad, I received this message.

SITUATION:  When I connected the iPad to iTunes, I got the message "iTunes has detected an iPad in recovery mode and must be restored".  After attempting the restore, I got the same message.  "The iPad cannot be restored. An unknown error occurred (21)."

TROUBLESHOOTING:  After updating iTunes, my PC's Windows, and making sure the cable I was using was working properly (it worked to update the other iPad), I called Apple Support.

SOLUTION:  According to the representative, 95% of the time unknown error 21 (assuming all of the above items are working properly), is a hardware problem.  I took my iPad back to Verizon and got a replacement unit. 

Hope this helps.

最后更新：2017-09-24 08:32:32

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