I had exactly the same problem, is because of the 4kstacks, i have a FC2 test3 release and it has that problem, i dont know if the if you can still recompile your kernel without the 4kstacks, but what i had to do, was install a 2.6.5 kernel, downloaded from kernel.org because the fedora kernel wont allow you to disable the 4kstacks so... i recommend download a 2.6.5 kernel from kernel.org and compile it withouth the 4kstacks and thats it.