[CentOS] Server rebooted, log message "kernel: Keepalive, Event:mdseve_cookie, client ping timeout"

Hi.   Our CentOS 5.4 server just rebooted sponteneously while doing heavy I/O.

There is a message in /var/log/messages just prior to reboot,

        kernel: Keepalive, Event:mdseve_cookie, client ping timeout

Google does not turn up anything.   What does this mean and how can I prevent
it from happening again, please?

Best,
-at