I get the following error when I try and save to MBR in Grub Customizer.
It used to work OK, it there something I need to do to make changes to the Grub Menu stick?
Start Terminal and load your file browser (I use Dolphin) with the following command
sudo dolphin /usr/sbin/
Navigate to the file grub-bios-setup, right click on the file name and select permissions. Make sure that the file has the correct permissions: