Help interpreting Machine Check Exception

[Andrew Walrond <andrew@walrond.org>]

This is a dual opteron numa machine and I am seeing messages like this during 
boot:

CPU 0: Machine Check Exception:               4 Bank 4: b200000000070f0f
TSC b961d94950
kernel panic - not syncing: Machine check

Which when run through Dave Jones tool says

andrew@orac test $ ./a.out -b 4 -s b200000000070f0f -e 4 -a 0
Status: (4) Machine Check in progress.
Restart IP invalid.
parsebank(4): b200000000070f0f @ 0
        External tag parity error
        CPU state corrupt. Restart not possible
        Error enabled in control register
        Error not corrected.
        Bus and interconnect error
        Participation: Generic
        Timeout:
        Request: Generic error
        Transaction type : Invalid
        Memory/IO : Other


Any clues on what might be broken? does "Bus and interconnect error" suggest 
the MB?

I have reseating all memory and cpus, and run memtest overnight without error.

Andrew Walrond