Io Firewire connection dropped on G5

Has anyone else experienced a dropped Firewire connection issue (Firewire indicator light on the front of the Io goes out) when playing back from the timeline in FCP 4.0.2? It seems to occur randomly but I cannot consistently play through a clip of more than a minute or two - no FX or layers. It appears to happen more frequently with 10 bit than 8 bit material.

I get dropped frames warnings when this happens, but I'm not sure if the dropped frames are causing the lost Firewire connection or if the lost Firewire connection is causing the dropped frames.

I've tried a different cable, and a different Firewire port.

G5 Dual 2GHz, 2.5GB RAM, 14 drive - XServeRAID, FCP 4.0.2, QT 6.4.

Thanks in advance.

Chip