Error 21 restoring iPhone4

[keratos]

Got given an iPhone to repair. Dont know the history on this handset.

Basically when powering on the apple logo appears then after about 8 seconds the phone reboots and the logo reappears then a reboot and so on. Stuck in this loop.

On my Windows 7 home premium laptop I downloaded redsn0w 9.12b2 and put the handset into PWNG DFU using redsn0w then tried to restore via iTunes but got Error 21.

Searched the forums and tried the following suggestions:

- Tried from another PC.
- Installed latest version of iTunes.
- Updated all drivers of the PC to latest.
- Turned off antivirus and Firewall
- Commented out lines in the hosts file


None of the above makes any difference. Still Error 21.

Help please

edit: I also tried "Fix Recovery" in redsn0w but the error "Missing keys.plist data for this build" appeared after it rebooted the phone??

[Yumraaj]

Read this.

[iPhone] IPhone 4 Restore Problem (Error 21) - MacRumors Forums

[keratos]

Originally Posted by Yumraaj

Read this.

[iPhone] IPhone 4 Restore Problem (Error 21) - MacRumors Forums

Got to the "Detecting IOS" in iFaith and error message "Unknown IOS" then the program aborts. So this didnt work. I guess the IOS is corrupt, thats why I am trying to restore in iTunes but its not having any of it for the reasons in the OP

[joecef]

Error 21 is possible bad battery. Just sayn

[southern128]

At times I get errors in itunes when trying to restore. What I do is, delete the host file. Works every time. Restore successfully and the host file comes back. If everything else does not work, try that.

[keratos]

Battery is fine

Host file fix already tried as mentioned in my OP above

[Yumraaj]

Try downloading another copy of the ios firmware and try again.

[keratos]

Tried that.
No difference
The ipsw works on another handset i have

[southern128]

everytime i have any error, i just delete the host file and restore. it works everytime. if u havent did that option, try it. delete and make sure its deleted before you plug in and restore.

[keratos]

as I said, the host file deletion. commenting out and so on have been tried to no effect

[InSaNiTy]

Do you have tiny umbrella installed ? If you do open Tiny Umbrella
Go to advance tab in TU and uncheck : set hosts file to cydia and close TU.
this is just to make sure you are letting apple verify your restore.
Just an idea since i haven't seen it posted yet, its worked for me in the past,
and hopefully it works for you!


Sorry Yumaai, I just clicked on you link .
I apologize!

[keratos]

TU made no difference.

I am a software engineer and would love a copy of the iTunes source code and library headers to debug this.

Anyway, what I have managed to find looking through apple documentation over the net is :

* Error -21 relates to an I/O level error, the IOSYS error is "badUnitErr"

* badUnitErr refers to the 0 (False) return code from a software lookup into the Unit Table using a driver reference taken from a given memory location.

* The Unit Table contains a list of all hardware drivers that have been loaded by iOS

* So what this means is that a software component is attempting to communicate with a hardware driver that does not exist.

What this means at the iTunes level is speculative because I do not have iTunes source code. But the likely candidates are:

* a corrupt driver on the PC - unlikely because I have used the PC to flash my other iPhone

* corrupted NVM or ROM code containing an erroneous pointer. This pointer is being used as a reference into the Unit Table but it refers to a non-existent hardware driver - possible if the handset is damaged (water , static, electrical etc.). Such an error would likely exist on the memory chips within the control board but could equally be contained within any component onto which memory store chips are held.


The upshot of this is that I am inclined to conclude that error -21 relates to a hardware failure in the iPhone, very likely to be the result of control board damage/failure but potentially a failure in one of the other handset components. Without more specific test equipment it is impossible to debug

[joecef]

"potentially a failure in one of the other handset components"

meaning it could be dock connector or headphone jack etc.. ??

i have 3gs with 21 and one with 28...goddamn useless paperweights right now

[wesboy]

Sounds like a defo hardware issue, I battled with my wifes ip4 for a couple ao days and gave up. Luckily when i took the phone to Apple they agreed and as the phone was in warranty, gave us a replacement. Granted this prob wont help you but thought I would share our experience with this error...........

[nickole214]

Originally Posted by keratos

Got given an iPhone to repair. Dont know the history on this handset.

Basically when powering on the apple logo appears then after about 8 seconds the phone reboots and the logo reappears then a reboot and so on. Stuck in this loop.

On my Windows 7 home premium laptop I downloaded redsn0w 9.12b2 and put the handset into PWNG DFU using redsn0w then tried to restore via iTunes but got Error 21.

Searched the forums and tried the following suggestions:

- Tried from another PC.
- Installed latest version of iTunes.
- Updated all drivers of the PC to latest.
- Turned off antivirus and Firewall
- Commented out lines in the hosts file


None of the above makes any difference. Still Error 21.

Help please

edit: I also tried "Fix Recovery" in redsn0w but the error "Missing keys.plist data for this build" appeared after it rebooted the phone??

are you familiar for the restore error 1..? my iphone 4s error 1 pls help me..

[hope376]

I remember getting this error on 3g handsets. Sometimes changing the battery or at least using a fully charged battery can over come this problem. I also heard you should disconnect the battery for a couple of minutes.

This is a hardware error and sometimes can be fixed or OOSW with crapple.

[nhoy2011]

Originally Posted by Yumraaj

Read this.

[iPhone] IPhone 4 Restore Problem (Error 21) - MacRumors Forums

thank you for directing me at the site..had that problem and now i can have clean restore..thanks again

[southern128]

it just so happen, i received error 21 just now and i thought about this thread. as soon as i saw

error 21, went to t C:\Windows\System32\drivers\etc and deleted the host file, tried the

restore again, went through like normal. i posted this already, instead of trying to figuire why

and what is causing the problem, just delete the host file. if that dont work, spend hours and all

day trying to find the solution. there is never just one way for any problem.

what