Could not update to 20.04

[Ayush Oberoi]

When I try to upgrade my 18.04 ubuntu to 20.04, it shows the error "could not calculate upgrade size".

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.41
ProcVersionSignature: Ubuntu 4.15.0-128.131-generic 4.15.18
Uname: Linux 4.15.0-128-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.20
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Sat Dec 12 15:40:30 2020
DistributionChannelDescriptor:
 # This is a distribution channel descriptor
 # For more information see http://wiki.ubuntu.com/DistributionChannelDescriptor
 canonical-oem-somerville-xenial-amd64-20160624-2
InstallationDate: Installed on 2019-10-05 (433 days ago)
InstallationMedia: Ubuntu 16.04 "Xenial" - Build amd64 LIVE Binary 20160624-10:47
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2020-12-12 (0 days ago)
mtime.conffile..etc.update-manager.release-upgrades: 2020-11-16T19:42:23.145909