The same thing happened to me when running upgrade-from-grub-legacy.
I think the problem was that I needed to choose the drive where to setup grub2 in a ncurses dialog:
[ ] /dev/sda
I selected /dev/sda using the keyboard arrows and then I pressed "ENTER". Everything seemed to be OK, until I rebooted and got the same error as you. I think that probably, I should have checked the checkbox with SPACE before hitting ENTER key:
[X] /dev/sda
If this is really the reason why I experience the problem, I think the ncurses dialog should check if at least one drive was actually selected before continuing. This is even more annoying because I have only one drive anyway.
I might be wrong that the problem might not be due to this but I think it would be best if someone checked.
The same thing happened to me when running upgrade- from-grub- legacy.
I think the problem was that I needed to choose the drive where to setup grub2 in a ncurses dialog:
[ ] /dev/sda
I selected /dev/sda using the keyboard arrows and then I pressed "ENTER". Everything seemed to be OK, until I rebooted and got the same error as you. I think that probably, I should have checked the checkbox with SPACE before hitting ENTER key:
[X] /dev/sda
If this is really the reason why I experience the problem, I think the ncurses dialog should check if at least one drive was actually selected before continuing. This is even more annoying because I have only one drive anyway.
I might be wrong that the problem might not be due to this but I think it would be best if someone checked.