After upgrading some machines to SLC3, would get this error message during boot. The solution was to add the following to the kernel lines in /etc/grub.conf:

apm=off noapmd acpi=off noacpi

The kernel lines then read as:

kernel /vmlinux-2.4.21-27.0.2.EL.cernsmp ro root=LABEL=/ apm=off noapmd acpi=off noacpi