You're exceeding the specs for the length of firewire, which is 4.5M. Check the link supplied:
What you could do is use firewire in conjunction with a "repeater box" or a device that basically strengthens the signal and pushes it further on a "long run cable". So 100' is far too long a cable for typical firewire use. check link:
100' firewire causing my computer to crash? I have a camcorder hooked up to my Mac computer at school to record demonstrations. I have had to get 2 new computers in the last 2 years. Tech says that the firewire is at fault and suggests I get a new camera with a different wiring. I no longer use my camcorder and haven't had the problem. Any comments or ideas on this?