There are no error messages in any logs. For example, in /var/log/messages, everything looks normal until you see the kernel restart messages after the reboot, although there seems to be a long gap in time between the last entry and the time when the systems actually stopped and was restarted. Whatever is happening, the system doesn't seem to be in a state where the problem can be recorded.
By the way, I forgot to list my kernel version. uname -rmi gives: 2.6.18-194.32.1.el5 x86_64 x86_64
Can you install RHEL and see if it goes away? Otherwise, open a ticket with RedHat...
Rainer