i am getting error while upgrade=ing ubuntu from 18.04 to 20,04 via upgrade manager

[jyotsna patil]

 i am getting error while upgrade=ing ubuntu from 18.04 to 20,04 via upgrade manager:

Could not calculate the upgrade

An unresolvable problem occurred while calculating the upgrade.

 This was likely caused by:
 * Unofficial software packages not provided by Ubuntu
Please use the tool 'ppa-purge' from the ppa-purge
package to remove software from a Launchpad PPA and
try the upgrade again.

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 1:18.04.42
ProcVersionSignature: Ubuntu 5.4.0-64.72~18.04.1-generic 5.4.78
Uname: Linux 5.4.0-64-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.21
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Wed Jan 27 23:05:14 2021
InstallationDate: Installed on 2020-03-10 (323 days ago)
InstallationMedia: Ubuntu 18.04.4 LTS "Bionic Beaver" - Release amd64 (20200203.1)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2021-01-27 (0 days ago)
VarLogDistupgradeTermlog:

[Brian Murray (brian-murray)]

Reviewing the files from your upgrade attempt you have installed nodejs from a location other than the offical Ubuntu archive. This version of nodejs is greater than the one in the official archive and is keeping some python packages installed which then prevents the upgrade from being calculated. Please remove nodejs along with any other packages from that archive and disable the archive. After that you can try upgrading again and if it still fails open a new bug report. Thanks and good luck!