itunes error 21

[dik]

Take a look here and there

[edinhox]

try to re-install it

[bacardi]

You need to use ireb or tiny umbrella (or possibly recboot) to get your phone out of dfu mode. The error is caused by to trying to restore a phone with custom firmware. To over come the error you need to put your phone dfu mode, and use ireb to fix the itune error before you restore.

Here are some instructions

Step 1: Start iTunes and put your phone into DFU mode:
Press and hold the Home button and the Power button at the same time. After exactly 10 seconds release the Power button. Continue holding the home button until you iTunes pops up a message telling you that it has detected an iPhone in recovery mode. At this point your iPhone/iPod touch screen will remain black.

Step 2: Now close iTunes and Start iREB on Windows.

Step 3: Simply select your device and wait for a few seconds until you get white or a red screen on your iPhone or iPod touch.

Step 4: Now open iTunes and select your phone from the sidebar in iTunes. Now press and hold left alt; button (Shift; button on Windows) on the keyboard and then click on;Restore; (Not;Update) button in the iTunes and then release the Shift; button. Select a custom .ipsw file and restore it.

[stuck recovery mode]

stuck in recovery mode

After 2 days of trying everything to get my jailbroken iphone 4 out of this ?stuck in recovery mode? situation, which evolved from unable to upgrade/restore from ios 4.2.1 to ios 5.0.1 , I cured the problem basically as per the instructions on Exit iOS 4.3.3 Recovery Mode Loop Using TinyUmbrella (Fix Recovery) | Jaxov I did however download the Zlib1.dll from a more reputable site than the one suggested ? google it.

The problem turned out to be twofold. Firstly apple has introduced a security check which caused the recovery mode. This was made worse by settings left over from previously saving my shsh blobs.

Basically the solution is the following:

Step 1 get out of recovery mode by:
I downloaded the tinyumbrella ?fix recovery? program ? note this is not the standard tinyumbrella program. Use the proper tinyumbrella site.
I downloaded the Zlipl.dll file and put it in the same folder as the ?fix recovery program
Have internet running in background
Launch itunes plug in phone, let itunes run in background
Put phone into dfu mode (google it) this was not easy( I do know dfu mode well and use it often) due to being stuck in recovery mode loop but several repeated attempts got the apple logo for a split second and several attempts at coordinating it I was able to launch fixrecovery421.exe at exactly this moment. This was the hardest part.
When you see ?exiting libpoison? disconnect phone. Now you have your phone back!

If this didn?t work you could also try download and run latest standard tinyumbrella ( I used v5.10.03) and untick ?set hosts to cydia on exit? on ?advanced tab? then click
?exit recovery? button while in momentary dfu mode as described above.

Step 2 correct settings on phone to satisfy apple servers:
Now download and run latest standard tinyumbrella ( I used v5.10.03) and untick ?set hosts to cydia on exit? on ?advanced tab?
Now go to itunes and do your ?restore? again. It works!