If you upgraded from Fedora 16 to Fedora 17, you may get an error when shutting down the system.
This happens because the kernel is the same, and grub2.cfg does not get the Fedora 17 kernel, but it is installed, although not recognized.
To fix this just run the following command:
# grub2-mkconfig > /etc/grub2.cfg && grub2-install /dev/sda
Notice that you should change /dev/sda for your partition
This will generate a new grub2.cfg with the new Fedora 17 kernel.