Hi, I have a Canon 9950F scanner and an external G-Technology 1TB HD. I connect them through Firewire (800 for the HD and 400 for the scanner) and can use either of them separately with no problem, but recently I tried to use them simultaneously and found out that turning on the HD while using the scanner interrupts communication with the scanner. This happens with both a 2008 Mac Pro or a 2008 MBP. Apple says this could be caused by the Canon scanner driver. Canon says it is an Apple problem. I can get around by connecting either peripheral through USB but I prefer to use the FW connections (800 for the HD and 400 for the scanner). Any thoughts? Thanks.