VISTA forgets 1394 Acknowledge Code

We are having troubles getting an audio device, which works fine together
with Windows XP, to run with Windows VISTA. What happens is that after a
short while VISTA removes the driver, claiming it got a "Surprise Removal",
which isn't right.

Now I have had a FireSpy to check the communication on the 1394 FireWire
bus, and it shows, that VISTA suddenly forgets to send "ack_complete"
Acknowledge Code as response to a Read Response from the device.

As far as I can find out the receiver must send the Acknowledge Code within
"ack gap" = 40 nS.

Has anybody else seen this behaviour? Is there a fix for the problem?

Thanks in advance

Eigil