Hi everyone, I was downgrading to the 10.5.5 version of IOUSBFamily (I'm running 10.5.6) from here: http://developer.apple.com/hardwaredrivers/download/usbdebug.html . Unfortunately, after doing this my system panics when it boots. Even single user mode doesn't work as the IOUSBFamily is incorrect. Luckily, I have a Windows partition that I have booted in to, and I have downloaded MacDrive so I can access my Mac Partition. Could someone with 10.5.6 please upload their IOUSBFamily.kext found in System/Library/Extensions/ ? If I can copy this back on to the Mac drive in the correct location then I think it should start booting again. Thanks!