sudo upgrade-manager -d crashes on update attempt

[David Kastrup]

Here is the error output:
$ sudo update-manager -d

(update-manager:16978): dbind-WARNING **: 16:32:59.558: Couldn't connect to accessibility bus: Failed to connect to socket /tmp/dbus-DUH5f3BRKD: Connection refused
WARNING:root:can not import unity GI Namespace Dbusmenu not available
Checking for a new Ubuntu release

(python3:17891): dbind-WARNING **: 16:33:28.026: Couldn't connect to accessibility bus: Failed to connect to socket /tmp/dbus-DUH5f3BRKD: Connection refused
/usr/lib/python3/dist-packages/DistUpgrade/DistUpgradeFetcher.py:23: PyGIWarning: Gtk was imported without specifying a version first. Use gi.require_version('Gtk', '4.0') before import to ensure that the right version gets loaded.
  from gi.repository import Gtk, Gdk
Traceback (most recent call last):
  File "/usr/bin/do-release-upgrade", line 168, in <module>
    fetcher = get_fetcher(options.frontend, m.new_dist, options.data_dir)
  File "/usr/bin/do-release-upgrade", line 33, in get_fetcher
    _("Downloading the release upgrade tool"))
  File "/usr/lib/python3/dist-packages/DistUpgrade/GtkProgress.py", line 34, in __init__
    self.widgets = SimpleGtkbuilderApp(uifile, "ubuntu-release-upgrader")
  File "/usr/lib/python3/dist-packages/DistUpgrade/SimpleGtk3builderApp.py", line 33, in __init__
    self.builder.add_from_file(path)
GLib.Error: gtk-builder-error-quark: /usr/share/ubuntu-release-upgrader/gtkbuilder/AcquireProgress.ui:6:36 Invalid property: GtkWindow.border_width (11)

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.21
ProcVersionSignature: Ubuntu 4.15.0-29.31-lowlatency 4.15.18
Uname: Linux 4.15.0-29-lowlatency x86_64
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
CrashDB: ubuntu
Date: Mon Jul 30 16:34:45 2018
InstallationDate: Installed on 2011-10-14 (2481 days ago)
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release i386 (20111011)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
Symptom: ubuntu-release-upgrader
UpgradeStatus: No upgrade log present (probably fresh install)
VarLogDistupgradeAptHistorylog:
 Start-Date: 2018-07-12 12:38:22
 Requested-By: dak (1000)
 Remove: navit-gui-internal:amd64 (0.5.0+dfsg.1-2build1)
 End-Date: 2018-07-12 12:38:23
VarLogDistupgradeTermlog:

mtime.conffile..etc.update-manager.release-upgrades: 2018-04-05T21:30:42.599279