package grub-pc 2.02-2ubuntu8.6 failed to install/upgrade: Unterprozess installed grub-pc package post-installation script gab den Fehler-Ausgangsstatus 2 zurück

still unsolved

ProblemType: Package
DistroRelease: Ubuntu 18.04
Package: grub-pc 2.02-2ubuntu8.6
ProcVersionSignature: Ubuntu 4.15.0-21.22-generic 4.15.17
Uname: Linux 4.15.0-21-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.4
AptOrdering:
 libkpathsea6:amd64: Install
 NULL: ConfigurePending
Architecture: amd64
Date: Fri Oct 12 10:22:31 2018
ErrorMessage: Unterprozess installed grub-pc package post-installation script gab den Fehler-Ausgangsstatus 2 zurück
InstallationDate: Installed on 2016-05-08 (886 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
InvalidGrubScript: /etc/default/grub
ProcCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.15.0-21-generic root=UUID=d05202f5-c1ac-4323-aba9-0e7bd6543243 ro plymouth:debug drm.debug=0xe
Python3Details: /usr/bin/python3.6, Python 3.6.6, python3-minimal, 3.6.5-3ubuntu1
PythonDetails: /usr/bin/python2.7, Python 2.7.15rc1, python-minimal, 2.7.15~rc1-1
RelatedPackageVersions:
 dpkg 1.19.0.5ubuntu2
 apt 1.6.5
SourcePackage: grub2
Title: package grub-pc 2.02-2ubuntu8.6 failed to install/upgrade: Unterprozess installed grub-pc package post-installation script gab den Fehler-Ausgangsstatus 2 zurück
UpgradeStatus: No upgrade log present (probably fresh install)