The problem is simply that you had edited your /etc/default/grub file and inserted some invalid text on this line:
GRUBboo# If you change this file, run 'update-grub' afterwards to update
Purging and reinstalling restored this file.
The problem is simply that you had edited your /etc/default/grub file and inserted some invalid text on this line:
GRUBboo# If you change this file, run 'update-grub' afterwards to update
Purging and reinstalling restored this file.