I'm running Ubuntu 14.04.4 and just tried unsuccessfully to upgrade to 16.04.1. 14.04 has been reliable, but 16.04 is being less than hospitable!
sudo do-release-upgrade, and it falls over in exactly the way described in this thread (dating from the days of 13.10), complete with unhelpfully vague error message.
grep Broken /var/log/dist-upgrade/apt.log to find broken packages, as the top-rated answer suggests, and generate a list of over 900 broken packages!
Other information I have available:
sudo dpkg -l | grep -w "rc"
sudo rename 's/\.list$/.list.disable/' /etc/apt/sources.list.d/*.list && sudo aptitude update && aptitude search '?narrow(?installed, !?archive(trusty))'
Mostly these are a bit of a wall of text, hence attempting to use pastebin -- stymied by lack of reputation, apparently. I can post anything needed as a comment.
Before I consider installing 16.04.1 over the top of 14.04, is there anything I should try in order to get the release-upgrade method to work? Or is my system now sufficiently riddled with third-party stuff (particularly, things installed to get other bits of software working / deal with inadequate driver support etc.) that I should bite the bullet and do a clean install? -- or junk it and stick with 14.04...