This seems to be an install on regular hardware, correct? This error is reported 3 times now, so far not able to find the cause.
Do you still have the install (since the install went successfully, just the bootloader is not there yet)? It is fully usable once grub is installed. If you are willing to help debug, then please use the ISO from which you did this install and go back to Live mode. Then chroot into the install:
Once chrooted install grub:
sudo grub-install /dev/sda
If this is successful, next run:
sudo grub-mkconfig -o /boot/grub/grub.cfg
but probably the first command will result in errors, please post the complete output of that error, including the command used.