I've never worked with Sun hardware, but I have seen an HP-UX box halt with parity errors, and I've had at least one Linux box go down with parity errors. In the cases that I have seen, they are caused by the memory - either it's bad, not seated correctly, or the heat got to them (in the case of my decrepit Linux box, my fan busted, and my memory fried even before my CPU).

I don't know where PCI0 is physically, but if you can find out, I bet that would lead you to the problem.