Some third party entries in your sources.list were disabled

[Ilya]

When I try upgrade Ubuntu 16.10 to 17.04
I get a message "Third party sources disabled..."
sudo add-apt-repository ppa:tualatrix/ppa
sudo apt-get update
sudo apt-get install ubuntu-tweak
update-manager -d
sudo apt-get install update-manager-core
do-release-upgrade -d
sudo apt-get dist-upgrade

Some third party entries in your sources.list were disabled. You can
re-enable them after the upgrade with the 'software-properties'...

ProblemType: Bug
DistroRelease: Ubuntu 17.04
Package: ubuntu-release-upgrader-core 1:17.04.10
ProcVersionSignature: Ubuntu 4.10.0-43.47-generic 4.10.17
Uname: Linux 4.10.0-43-generic x86_64
ApportVersion: 2.20.4-0ubuntu4.10
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: XFCE
Date: Tue Jan 23 03:50:39 2018
InstallationDate: Installed on 2017-09-19 (125 days ago)
InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to zesty on 2018-01-23 (0 days ago)
VarLogDistupgradeAptlog:
 Log time: 2018-01-23 03:26:45.345949
 Log time: 2018-01-23 03:26:49.487077
 Log time: 2018-01-23 03:39:17.202064