do-release-upgrade from 14.04 to 16.04 fails on HP Microserver

[Mike Tubby]

root@public:/www# do-release-upgrade
Checking for a new Ubuntu release
Get:1 Upgrade tool signature [198 B]
Get:2 Upgrade tool [1,265 kB]
Fetched 1,265 kB in 0s (0 B/s)
authenticate 'xenial.tar.gz' against 'xenial.tar.gz.gpg'
extracting 'xenial.tar.gz'

... starts upgrade process

System is 'native' 14.04 LTS except for two packages installed from PPA:

1. Nginx webserver
2. Prosody IM server

installer says "Third party sources have been disabled - you can re-enable them later ..."

Calculating the changes ...

Failed to calculate the changes

Aborting.

Press 'x' to close the screen.

root@public:/www# lsb_release -rd
Description: Ubuntu 14.04.4 LTS
Release: 14.04

Mike

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubuntu-release-upgrader-core 1:0.220.8
ProcVersionSignature: Ubuntu 3.13.0-92.139-generic 3.13.11-ckt39
Uname: Linux 3.13.0-92-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.21
Architecture: amd64
CrashDB: ubuntu
Date: Thu Aug 4 22:28:14 2016
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_GB:en
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to trusty on 2016-08-04 (0 days ago)

[Mike Tubby (1fpb)]

The last line of the problem text:

UpgradeStatus: Upgraded to trusty on 2016-08-04 (0 days ago)

is misleading since the timestamp was reset when the upgrade to Xenial aborted ... the machine had actually been running 14.04 LTS from new (over 18 months) and had been updated regularly via:

    apt-get update
    apt-get dist-upgrade

Mike