Em este tópico de discussão , o usuário Paul Davis diz:
The problem from what I can tell is that grub2 was upgraded, however, during the install the grub image was installed to the wrong hard drive. The old grub2 image can't load the new grub2 modules so it fails. Luckily there is a really easy way to fix it, just boot from the hard drive that mistakenly had the new grub2 image installed on it. You can either change the boot drive in the BIOS directly or most BIOS's have a boot menu that lets you decide which drive to boot from. Once you get back into Ubuntu you can just do a sudo grub-install /dev/sdx where sdx is the drive that the the grub2 image should have been installed on to get everything fixed to the way it should have been.