[K12OSN] iMac booting intermittant

[Joe Guenther]

When trying to boot an iMac on the K12LTSP 5.0.0 beta5 with all updates, 
I somtimes get the

/pci/mac-io/ethernet::-1,yaboot.conf: Unknown or corrupt filesystem
Can't open config file
Welcome to yaboot version 1.3.10
Enter "help" to get some basic usage information
boot: _

Then it just sits there.  Occasionally it will boot properly.  This will 
be a REAL SHOWSTOPPER as I have been asked to demo this to Alberta zone 
5 & 6 school division technology meeting.  I can boot an iBook by 
holding down the N key on boot. A big part of this demo is to show how 
to recycle old junkers ... we have a ton of old iMacs that run great 
IF/WHEN they boot.

please help!
Joe Guenther