system failed, save tasks

[T.F. Cheng]

hi,
  i just got a weird computer voice, saying "system
failed, save tasks". the system is running 
FreeBSD  6.2-PRERELEASE FreeBSD 6.2-PRERELEASE #6: Sat
Dec  9 10:03:38 EST 2006    
root@:/usr/src/sys/i386/compile/TFCHENG  i386
i wondered what happened, i only have ssh running, and
there are some attempt of break-in as logged in the
auth.log, In the /var/log/message, before i rebooted
the system, the only messages were (on 12/25) :
Dec 25 20:59:40  kernel: sk0: link state changed to
DOWN
Dec 25 20:59:42  kernel: sk0: link state changed to UP
Dec 25 20:59:56  kernel: sk0: link state changed to
DOWN
Dec 25 21:00:00  kernel: sk0: link state changed to UP
Dec 25 21:00:12  kernel: sk0: link state changed to
DOWN
Dec 25 21:00:14  kernel: sk0: link state changed to UP
Dec 25 21:19:45  kernel: sk0: link state changed to
DOWN
Dec 25 21:19:50  kernel: sk0: link state changed to UP
Dec 25 21:19:50  kernel: NVRM: Xid (0001:00): 4,
Channel 00000001
Dec 25 21:19:50  kernel: ad6: TIMEOUT - WRITE_DMA
retrying (1 retry left) LBA=8598287
Dec 25 21:19:53  kernel: NVRM: Xid (0001:00): 8,
Channel 00000000
Dec 25 21:19:53  kernel: NVRM: Xid (0001:00): 4,
Channel 00000001

what might have happened? where should I look??

thanks!!

TFC

Best Regards,

Tsu-Fan Cheng

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