Upgrade 16.04 LTS to 18.04 LTS failed

[Mike]

System has been successfully running 16.04 for a long time. Although I have some PPAs configured and presumably this is breaking the upgrade, but there does not seem to be any way to determine which ones or how to go about making the upgrade possible.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.26
ProcVersionSignature: Ubuntu 4.15.0-43.46~16.04.1-generic 4.15.18
Uname: Linux 4.15.0-43-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.18
Architecture: amd64
CrashDB: ubuntu
Date: Sat Dec 29 19:40:19 2018
InstallationDate: Installed on 2014-01-21 (1803 days ago)
InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Release amd64 (20131016.1)
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_US
 TERM=xterm-256color
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2018-12-30 (0 days ago)