i had a problem very similar to this recently (same errors) and i couldnt fix it-- at the time i was too busy with other tasks. im not used to installed systems having hiccups in grub-- ive never run grub-mkconfig or grub-install directly either, but this:
grub-mkconfig > /mnt/grub/grub.cfg
grub-install --target=i386-pc /dev/sda --boot-directory=/mnt
could be useful, thank you. in the days before grub 2 it was always easy; install and edit, reboot. im still used to grub being reliable, just tedious.