Upgrade from 16.04 to 17.04 crashes with info, that I might use test version

excerpt from /var/log/dist-upgrade/main.log:
2017-11-11 20:31:47,758 DEBUG entry 'deb http://security.ubuntu.com/ubuntu zesty-security multiverse' updated to new dist
2017-11-11 20:31:47,758 DEBUG examining: 'deb https://josm.openstreetmap.de/apt xenial universe'
2017-11-11 20:31:47,761 DEBUG entry '# deb https://josm.openstreetmap.de/apt zesty universe # wyłączony podczas aktualizacji do zesty' was disabled (unknown mirror)
2017-11-11 20:31:47,761 DEBUG examining: 'deb [arch=amd64] http://dl.google.com/linux/chrome/deb/ stable main'
2017-11-11 20:31:47,764 DEBUG entry '# deb [arch=amd64] http://dl.google.com/linux/chrome/deb/ stable main # wyłączony podczas aktualizacji do zesty' was disabled (unknown mirror)
2017-11-11 20:31:47,764 DEBUG examining: 'deb http://ppa.launchpad.net/nextcloud-devs/client/ubuntu xenial main'
2017-11-11 20:31:47,767 DEBUG entry '# deb http://ppa.launchpad.net/nextcloud-devs/client/ubuntu zesty main # wyłączony podczas aktualizacji do zesty' was disabled (unknown mirror)
2017-11-11 20:31:49,742 DEBUG running doUpdate() (showErrors=True)
2017-11-11 20:32:22,224 DEBUG openCache()
2017-11-11 20:32:22,225 DEBUG failed to SystemUnLock() (E:Niezablokowany)
2017-11-11 20:32:23,553 DEBUG /openCache(), new cache size 87498
2017-11-11 20:32:23,554 DEBUG need_server_mode(): run in 'desktop' mode, (because of pkg 'ubuntu-desktop')
2017-11-11 20:32:29,507 DEBUG Installing 'xserver-xorg-video-all' (Distro KeepInstalledPkgs rule)
2017-11-11 20:32:55,264 ERROR Dist-upgrade failed: 'E:Nie udało się naprawić problemów, zatrzymano uszkodzone pakiety.'
2017-11-11 20:32:55,272 DEBUG abort called
2017-11-11 20:32:55,274 DEBUG openCache()
2017-11-11 20:32:55,275 DEBUG failed to SystemUnLock() (E:Niezablokowany)
2017-11-11 20:33:01,368 DEBUG /openCache(), new cache size 85622

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.23
ProcVersionSignature: Ubuntu 4.4.0-98.121-generic 4.4.90
Uname: Linux 4.4.0-98-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.10
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Sat Nov 11 20:32:47 2017
InstallationDate: Installed on 2016-05-01 (558 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2017-11-11 (0 days ago)
VarLogDistupgradeTermlog:

mtime.conffile..etc.update-manager.release-upgrades: 2016-05-17T23:56:18.872768