I've been getting the same message on two SMP machines - AMD quad-core and Intel I7 - both under fairly heavy load at the time (CPU load)
The AMD is running FC11 with kernel 18.104.22.168-43.fc11.x86_64
The Intel i7 is running FC12 with kernel 22.214.171.124-162.fc12.x86_64
Kernel.org seems to think the fix is this patch http://git.kernel.org/tip/bfeed8fcf9...4e77fd49930e36
mentioned in this post http://bugzilla.kernel.org/show_bug.cgi?id=14289
but of course those of us using Fedora don't usually compile our own kernels. At this point I've nailed my AMD at full speed by turning cpuspeed off - so far this has at least delayed the onset. I've just done the same to the i7 - will report back if this fails. I expect it is not a solution - only getting the above patch in will be a solution.
I note that on the i7 which is remote and in a place I only have access to after calling for someone to unlock - sometimes as much as a day later - the system seems to reboot itself after a while (many hours). I once managed to have a "ps -ef | wc" command run and it appeared to reboot after the process table got full from cron events that started but never finished.