Three days ago, I was hacking my iPhone to the max and sure enough .. after installing "categories" to enable more aplications on the iPhone in folder alike structures, the phone crashed. Bad.

While I didnt actually looked forward to this, this would normally be solved by a restore.. Nops. By a jailbreak and a restore... Nops.

Somehow I was unable to get the phone in to DFU mode, the startingpoint of jailbreaking your iPhone. I could restore the phone towards the normal status (you always can!) but my first gen -not solded in Europe- was without an ATT contract so I had in fact an iBrick.

I tried more then two hours in two days to get get the phone into DFU. But everytime I did a restore form the DFU mode I got an error 1600, everytime I did the restore from recovry mode I got error 21.

Getting an device into DFU isnt rocket science: start iTunes, connect iPhone, hold power and home for 10 seconds, release power hold home, hold home for 10 seconds. Boom, you are in. It can take 3 or 4 tries but not 200. Ans I was underway of getting there.

Only after way to much time DFUing my iPhone and reading what I did wrong, I found -yes at /the/ source- that an Mac OSX 10.5.6 can not DFU restore an iPhone! Yes, the latest and geatest Apple OS X version as of this writing has a bug where you can not DFU your iPhone:

Fixing DFU mode on 10.5.6

As noted previously OS X 10.5.6 introduced a bug that affected the use of DFU mode. with some Macs. There have been previously published hacks and techniques to fix this, but here is another method that can be used to temporarily restore DFU functionality in order to use QuickPwn or PwnageTool.

1. You will need an account with ADC (Apple Developer Connection) this is free and takes a few minutes to sign up, you should read the terms and conditions carefully and you should only sign up if you are thinking of developing applications in the future - http://developer.apple.com/mac/
2. Download the disk image “IOUSBFamily-315.4-log.dmg” for Mac OS X 10.5.5 Build 9F33” (yes, that is a “5” in 10.5.5 - this is a developer debug package of the USB kernel extension).
3. Unplug non-vital USB equipment, such as external DVD writers, USB scanners, USB mass storage devices, at the most leave a Keyboard and Mouse connected.
4. Install IOUSBFamily-315.4.1.pkg from within the disk image
5. Reboot your system!
6. Perform necessary DFU activity with QuickPwn or PwnageTool.
7. Download the disk image “IOUSBFamily-327.4.0-log.dmg” for Mac OS X 10.5.6 Build 9G55”
8. Intall IOUSBFamily-327.4.0.pkg from within the disk image
9. Reboot your system!
10. Reattach your USB peripherals.

Source