THe iphone could not be restored an unknown error occured 21.

SOURCE: iPhone 3G Error 0xE8000001

I just had this problem and it turned out to be... It didn't like my iPod cable. Switched to the iPhone cable and it worked.
Seems to be an iPhone 2.0 prob, or 3g prob, since I was using the iPod cable to sync my old iPhone just fine.

SOURCE: iphone cannot restore with itunes

Try the following links:
http://amountaintop.com/error-1604-when-upgrading-your-iphone-version-1-1-1
http://support.apple.com/kb/TS1458

270rexton

• 782 Answers
• Posted on May 12, 2009

SOURCE: iphone will not restore

try respring it (central + power buttons together and then connect to iTunes in safe mode,choose full restore (it will erase everything but if you have back up can be restored).

SOURCE: im getting an unknown error (1611) when i try to

Hi there,

This error may indicate a hardware issue with your device. If the MAC address or the IMEI is the default value (00 499901 064000 0), this can also confirm a hardware issue, to find these go to settings, general & about.

If you can get an appointment in an Apple store they can try a "known good" network connection & connector and try to restore the phone for you but if not it looks like it may be a hardware issue within the phone. If your still withing your warrenty give Apple a ring they'll sort it for you.

SOURCE: an error occurred while restoring this iphone

You may have the wrong iTunes for that update (you need the newest iTunes in order to restore iPhone's). You might also be installed a outdated iOS, or a higher version than the device you are running can handle.