Comment 18 for bug 2049785

I got a Xenial ISO and run it in a virtual machine.

Enabled proposed and now upgrading update-manager forces the installation of a newer ubuntu-advantage-tools:

--->
$ sudo apt install update-manager --verbose-versions
Reading package lists...
Building dependency tree...
Reading state information...
The following additional packages will be installed:
   distro-info (0.14ubuntu0.3)
   python3-distro-info (0.14ubuntu0.3)
   python3-update-manager (1:16.04.20)
   python3-yaml (3.11-3build1)
   ubuntu-advantage-tools (31.2~16.04)
   ubuntu-pro-client (31.2~16.04)
   ubuntu-pro-client-l10n (31.2~16.04)
   update-manager-core (1:16.04.20)
Suggested packages:
   shunit2
The following NEW packages will be installed:
   distro-info (0.14ubuntu0.3)
   python3-distro-info (0.14ubuntu0.3)
   python3-yaml (3.11-3build1)
   ubuntu-pro-client (31.2~16.04)
   ubuntu-pro-client-l10n (31.2~16.04)
The following packages will be upgraded:
   python3-update-manager (1:16.04.17 => 1:16.04.20)
   ubuntu-advantage-tools (10ubuntu0.16.04.1 => 31.2~16.04)
   update-manager (1:16.04.17 => 1:16.04.20)
   update-manager-core (1:16.04.17 => 1:16.04.20)
4 upgraded, 5 newly installed, 0 to remove and 210 not upgraded.
Inst python3-yaml (3.11-3build1 Ubuntu:16.04/xenial [amd64])
Inst distro-info (0.14ubuntu0.3 Ubuntu:16.04/xenial-proposed [amd64])
Inst ubuntu-advantage-tools [10ubuntu0.16.04.1] (31.2~16.04 Ubuntu:16.04/xenial-proposed [all]) []
Inst ubuntu-pro-client (31.2~16.04 Ubuntu:16.04/xenial-proposed [amd64])
Inst ubuntu-pro-client-l10n (31.2~16.04 Ubuntu:16.04/xenial-proposed [amd64])
Inst python3-update-manager [1:16.04.17] (1:16.04.20 Ubuntu:16.04/xenial-proposed [all]) [update-manager-core:amd64 ]
Inst update-manager-core [1:16.04.17] (1:16.04.20 Ubuntu:16.04/xenial-proposed [all]) [update-manager:amd64 ]
Inst update-manager [1:16.04.17] (1:16.04.20 Ubuntu:16.04/xenial-proposed [all]) []
Inst python3-distro-info (0.14ubuntu0.3 Ubuntu:16.04/xenial-proposed [all])
Conf python3-yaml (3.11-3build1 Ubuntu:16.04/xenial [amd64])
Conf distro-info (0.14ubuntu0.3 Ubuntu:16.04/xenial-proposed [amd64])
Conf ubuntu-pro-client (31.2~16.04 Ubuntu:16.04/xenial-proposed [amd64])
Conf ubuntu-advantage-tools (31.2~16.04 Ubuntu:16.04/xenial-proposed [all])
Conf ubuntu-pro-client-l10n (31.2~16.04 Ubuntu:16.04/xenial-proposed [amd64])
Conf python3-update-manager (1:16.04.20 Ubuntu:16.04/xenial-proposed [all])
Conf python3-distro-info (0.14ubuntu0.3 Ubuntu:16.04/xenial-proposed [all])
Conf update-manager-core (1:16.04.20 Ubuntu:16.04/xenial-proposed [all])
Conf update-manager (1:16.04.20 Ubuntu:16.04/xenial-proposed [all])
<---

I confirm then that launching and finishing update-manager without internet connection produces no error any more.