Could 10.4.11 server upgrade be the problem?

[HSANOM]

I run a computer lab here using NetRestore and NetBoot to reimage my entire MAC lab (Intel and PPC). This has worked in the past however I encountered some problem with the PPC during the NetBoot stage. I have described the scenario below:

1) I have just updated the server to 10.4.11.
2) The Intel NetBoots just fine and I can reimage the Intel machines.
3) HOWEVER, the PPC machines I get this errors. On PPC running 10.4.8, I come across a symbol very similar to the 'no entry' traffic road signs during NetBoot AND another PPC running 10.4.11, I get this error message:

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Invalid memory access at %SRR0: 05610dec %SRR1: 00003030
Apple PowerBook6,5 4.8.7f1 BootROM built on 09/23/04 at 16:13:18
Copyright 1994-2004 Apple Computer, Inc.
All Rights Reserved.

Welcome to Open Firmware, the system time and date is: 19:53 01/15/2008
The battery capacity is: 99 percent

To continue booting, type "mac-boot" and press return.
To shut down, type "shut-down" and press return.
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Please help urgently... Thanks