I have a MB connected to a Lacie d2 Quadra 500Gb via firewire. When I run time machine it will back up only about 20Gb of 77Gb. I'll start time machine, it'll plug away, and when I come back, my computer logs off. When I log on, I see that time machine failed. I formatted my external HD, and tried running time machine again, and the same thing happens. Help, what is going?