Failure to upgrade from 16.04.6 LTS to 18.04, due to failing to calculate changes

[rollthedyc3]

lsb_release -rd

Description: Ubuntu 16.04.6 LTS
Release: 16.04

In /var/log/dist-upgrade/main.log, there is this error message:

2019-04-14 22:29:40,878 ERROR Dist-upgrade failed: 'E:Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages.'

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.26
ProcVersionSignature: Ubuntu 4.4.0-143.169-generic 4.4.170
Uname: Linux 4.4.0-143-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia_drm nvidia_modeset nvidia
ApportVersion: 2.20.1-0ubuntu2.18
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: i3
Date: Sun Apr 14 22:31:09 2019
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2019-04-15 (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.