Fedora 18 grub2-mkconfig error

I installed Fedora 18 in VirtualBox 4.2.12 and ran

yum install update

to Linux 3.8.8


I then edited /etc/default/grub to add the line:

GRUB_CMDLINE_LINUX_DEFAULT="acpi=force"

because my shutdownfor the vm in VirtualBox was hanging.

I the tried to run:

grub2-mkconfig -o /boot/grub2/grub.cfg

but i get an error saying "incorrect command", "incorrect syntax", and error at line 153.

Any help would be appreciated. Thanks in advance.