To resolve the iTunes Error 21 connect to your device in DFU mode first to get by following the instructions according to your device, you can get into DFU mode.
Connect your device to your PC or Mac via a USB cable and launch iTunes.
Hold Home + Power button for 10 seconds.
After 10 seconds release the power button off, but keep the Home button pressed until iTunes a little device in recovery mode you find there.
Once your device into DFU mode, you see nothing on the screen, only a black
Connect your device to your PC or Mac via a USB cable and launch iTunes.
Hold Home + Power button for 10 seconds.
After 10 seconds release the power button off, but keep the Home button pressed until iTunes a little device in recovery mode you find there.
Once your device into DFU mode, you see nothing on the screen, only a black