It looks very much like a hardware fault relating to either Your CPU/mainboard (K8 refering to AMD Early Opteron/Athlon/Turion era chipset) or a faulty memory module (ECC a type of server memory)
I would recommend running some general hardware diagnostics paying close attention to both those areas, though I cant suggest any specific apps to do so.
ns224295 kernel: Northbridge Error, node 0, core: -1
Message from syslogd@ at Thu Sep 15 23:01:12 2011 ...
ns224295 kernel: K8 ECC error.
Message from syslogd@ at Thu Sep 15 23:01:12 2011 ...
ns224295 kernel: Northbridge Error, node 0, core: -1
Message from syslogd@ at Thu Sep 15 23:01:12 2011 ...
ns224295 kernel: K8 ECC error.
Message from syslogd@ at Thu Sep 15 23:01:13 2011 ...
ns224295 kernel: Northbridge Error, node 0, core: -1
Message from syslogd@ at Thu Sep 15 23:01:14 2011 ...
ns224295 kernel: K8 ECC error.
Message from syslogd@ at Thu Sep 15 23:01:14 2011 ...
ns224295 kernel: Northbridge Error, node 0, core: -1
Message from syslogd@ at Thu Sep 15 23:01:15 2011 ...
ns224295 kernel: K8 ECC error.
Message from syslogd@ at Thu Sep 15 23:01:15 2011 ...
ns224295 kernel: Northbridge Error, node 0, core: -1
Message from syslogd@ at Thu Sep 15 23:01:16 2011 ...
ns224295 kernel: K8 ECC error.
Message from syslogd@ at Thu Sep 15 23:01:16 2011 ...
ns224295 kernel: Northbridge Error, node 0, core: -1
Message from syslogd@ at Thu Sep 15 23:01:17 2011 ...
ns224295 kernel: K8 ECC error.
I would recommend running some general hardware diagnostics paying close attention to both those areas, though I cant suggest any specific apps to do so.