Ian,
I can't seem to find much out about your HU in conjunction with the PhatBox.
What I have been able to find out, is that there have been a number of firmware updates for your head unit in general. I'd recommend you check these out in case they help to resolve any issues controlling the PhatBox.
If after this you still have a problem, you might try changing the RC files on your PhatBox for the level 10 logging ones - which may show something up. There are others here better suited to checking the logs and finding out what's wrong.
Give us another shout once you've tried the HU firmware updates.