DFU is a low, pre-boot state in which you need to put your iPhone or iPod Touch in order to jailbreak it for the first time. In the recent 10.5.6 update from Apple, this functionality was disabled to further try to prevent users from jailbreaking their iPhones and iPod Touch’s by displaying an error in iTunes. A fix was involved regarding several files being modded in order to allow this functionality back into iTunes. To install this, download the file below, extract it, and then run the Automator program inside of it. You will need to be logged in as an administrator and provide the password for your user account.

OS X 10.5.6 Fix (Rapidshare)