Hi... i have this problem.
I don't use the adat output, anyway the light of adat1 is flashing. and i can see and hear too a signal that seems to be in the "in 13" on my total mix windows.
I also tried to plug a toslink cable into the adat1 in. but the problem remains the same!
in the preference windows i've wordclock set as master, but the adat1 change the status from "unlock/lock" continuosly.
please help me.

The set up i'm using is:

Mac pro quad core running with snow leopard
FF800 - outputs 1 to 8 connected to the mackie 32.8
Logic studio 9

Thx to anyone could be help me!