Lombard won't boot from Panther CD

When I try to boot my Lombard from Panther CD's, it goes to open firmware with "Default Catch!, code=400 at %SRR0: 30800010 %SRR1: 40003030" I have googled my poor little fingers raw, and don't know what it's all about. I have replace the 256mb ram in the upper slot with something smaller (the 256mb stick in the upper slot causes a video issue when installing panther, so i thought maybe it was causing my current problem)

Am I just stuck with 10.2 or less?

Thanks in advance,

CM