According to posters to the site:
"Minutes ago, Apple released the new OS X 10.5.6 update. We have to put a Big Warning on this update, because it causes problems with DFU mode. So with the Update 10.5.6 you cannot Jailbreak or Unlock your iPhone / iPod Touch with PwnageTool or QuickPwn as on the newest MacBooks. Update your System only if you really need it!"
According to some, the workaround or fix is to replace some of the 10.5.6 frameworks with files from 10.5.5 overwriting the newer versions of the files in the kernel extension IOUSBFamily.kext. A safer workaround is to reinstall Mac OS X via an Archive and Install and upgrade it to 10.5.5.Resources