[X4U] G5 won't boot after target disk mode w/ OS9 G3

[Sam]

Brand new dual 2.0Ghz G5 running OS 10.3.5 and all updates. No classic mode
installed.

I booted it in firewire target disk mode and it mounted on the desktop of a
blue and white G3 just fine. Copied data from the G3 to the user's desktop
on the G5, shut everything down and disconnected.

The G5 now will not boot, giving the "no system folder" blinking question
mark. The hard drive is fine and will boot into target disk mode. I tried
repairing the disk and repairing permissions from the boot CD. Also tried
Diskwarrior, which gets to the last step and then finishes with a "Mac
services error. Try rebuilding again."

Any idea what happened? Any other option than reinstalling OS 10.3.5, either
on top or via archive and install? I was wondering if the disk didn't have
OS 9 drivers, but if it didn't, it wouldn't mount as a firewire drive under
OS 9, right? Something tells me I've read of this issue before, but I don't
know where or when.

-Sam