Upgrade from 18.04 through terminal not working

[RAJESH]

This was caused by:
* Upgrading to a pre-release version of Ubuntu
This is most likely a transient problem,
please try again later.
If none of this applies, then please report this bug using the
command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal. If
you want to investigate this yourself the log files in
'/var/log/dist-upgrade' will contain details about the upgrade.
Specifically, look at 'main.log' and 'apt.log'.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.40
ProcVersionSignature: Ubuntu 4.15.0-122.124-generic 4.15.18
Uname: Linux 4.15.0-122-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.9-0ubuntu7.19
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Tue Nov 10 13:46:13 2020
InstallationDate: Installed on 2019-02-19 (629 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
PackageArchitecture: all
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_IN
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2020-11-10 (0 days ago)
VarLogDistupgradeAptclonesystemstate.tar.gz:
 Error: command ['pkexec', 'cat', '/var/log/dist-upgrade/apt-clone_system_state.tar.gz'] failed with exit code 127: polkit-agent-helper-1: error response to PolicyKit daemon: GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: No session for cookie
 Error executing command as another user: Not authorized

 This incident has been reported.

[Brian Murray (brian-murray)]

Reviewing the files from your upgrade attempt you seem to have enabled a PPA that provides sane packages. This will prevent the upgrade as that PPA contains package version numbers greater than the release to which you are upgrading. You can revert the PPA by installing the ppa-purge package from the official Ubuntu archive and then running 'sudo ppa-purge ppa:sane-project/sane-git' or 'sudo ppa-purge ppa:sane-project/sane-release' . After that you can try upgrading again and if it still fails open a new bug report. Thanks and good luck!