I've upgraded to Redhat 7 recently (from 6.2 and then 6.1). When I select "Halt" or "Reboot" from the GNOME log off menu (while logged in as root), all processes will shut down and the kernel will panic saying "attempted to kill the idle task". "Shutdown -r now" and "shutdown -h now" work fine though.
Please provide the Oops information that appears before the 'killing idle task' message. That is the important bit (moved to kernel, gnome cannot cause a crash unless the kernel is buggy...)
No reply in over a month, assuming APM/BIOS problem.