dpkg: error processing package ca-certificates

[Erik]

On upgrade from 14.04.05 to 16.04.2 using do-release-upgrade, I got this error:

dpkg: cycle found while processing triggers:
 chain of packages whose triggers are or may be responsible:
  man-db -> systemd
 packages' pending triggers which are or may be unresolvable:
  ca-certificates: update-ca-certificates
  man-db: /usr/share/man
  systemd: /etc/init.d
dpkg: error processing package ca-certificates (--remove):
 triggers looping, abandoned
ERROR: Cannot create report: [Errno 17] File exists: '/var/crash/ca-certificates.0.crash'
Error in function:

Upgrade was not successful, lsb_release -a reported 16.04.02 but the system was obviously not fully upgraded, and the network adapter was disabled according to lshw. Couldn't get online to try and repair so rolled back to a previous snapshot.

ubuntu-release-upgrader-core:
  Installed: 1:0.220.9