Been running my macbook pro and FF8oo for 3 years with no problems.

I have been using the firewire 400 port to run the FF800 and firewire 800 port to run my external hardrive.

Last week out in a church recording a brass band using 4 phatom powered mics when all the LED's on the FF800 stared to flash pretty patterns and my mac crashed. After a re start i noticed the host light was comming on every 2 or 3 minutes for a few seconds at a time and causing the recorded audio to stutter and glitch whilst the host light was on . I have had no more colourfull light shows and crashes but the host LED still persists with its flash causing a few second gap in playback audio or glitch in recorded audio.

After experimenting with different combinations and ruling out leads i have found the Fireface 800 using firewire 800 and my hardrive on firewire 400 works perfectly but switching it round causes the host  light flash. Also runnng on firewire 400 without my hardrive  the fireface does not flash and drop out. 

Im running logic 9 on snow leopard  with the latest rme firmware and driver versions.

Whats to blame. mac, hard drive or fireface 800 ?

Any wisdom gratefully received.