My mid-2007 iMac refuses to recognize an external WD My Book Studio 500 GB on FW connectivity ("Unknown device"). With USB it works fine. The weird part is that I have two of these drives and the other works perfectly! I had the other replaced but it is the same. I also have a Maxtor FW drive that works flawlessly. I have tried every trick I could google and without results. I am very frustrated at this at the moment! I have 10.5.2. Tried to reinstall but the combo updater says my hard drive does not meet the requirements. Thanks for not telling what those are.