Unable to install grub - Ubuntu 20.10 installation fail

[florin]

Ubuntu 20.10 fails installing because just at the end of the installation, grub-install /dev/sda fails without any obvious reason. I have both Windows 10 and Ubuntu 20.04 on the drive and had many previous versions before. It is the first time I get this error and I am glad I did foresee problems, always keeping another version of Ubuntu.

This is a Toshiba laptop about 4 years old, usually everything works flawless on it.

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: ubiquity 20.10.13
ProcVersionSignature: Ubuntu 5.8.0-25.26-generic 5.8.14
Uname: Linux 5.8.0-25-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu50
Architecture: amd64
CasperMD5CheckMismatches: ./pool/main/s/setserial/setserial_2.17-52_amd64.deb
CasperMD5CheckResult: skip
CasperVersion: 1.455
CurrentDesktop: ubuntu:GNOME
Date: Sun Oct 25 02:45:33 2020
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntu.seed maybe-ubiquity quiet splash ---
LiveMediaBuild: Ubuntu 20.10 "Groovy Gorilla" - Release amd64 (20201022)
ProcEnviron:
 LANGUAGE=en_US.UTF-8
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 LC_NUMERIC=C.UTF-8
RebootRequiredPkgs:
 linux-image-5.8.0-25-generic
 linux-base
 linux-base
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)