Change Desktop Background hangs, making System Settings (unity-control-center) inoperable

[Marcus Sundman]

First right-click on the desktop and choose "Change Desktop Background". Nothing happens. After that System Settings refuse to show.
E.g.:
$ unity-control-center
Failed to register: Timeout was reached
$

Ubuntu Release: 14.10
Package Version: 14.10.0+14.10.20140922-0ubuntu2

ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: unity-control-center 14.10.0+14.10.20140922-0ubuntu2
ProcVersionSignature: Ubuntu 3.16.0-20.27-generic 3.16.3
Uname: Linux 3.16.0-20-generic x86_64
ApportVersion: 2.14.7-0ubuntu2
Architecture: amd64
CurrentDesktop: Unity
Date: Thu Oct 2 18:51:36 2014
InstallationDate: Installed on 2013-11-27 (309 days ago)
InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Release amd64 (20131016.1)
SourcePackage: unity-control-center
UpgradeStatus: No upgrade log present (probably fresh install)

[William Lee (wlee753159)]

Can you still open the Unity Control Centre from Power and Settings Button > System Settings..?

[Marcus Sundman (sundman)]

It's the "unity-control-center appearance" which hangs when I right-click on the desktop and choose "Change Desktop Background". After that unity-control-center won't start. Neither from the top-right-button menu nor from the shell.
A "killall -HUP unity-control-center" fixes it.

[Launchpad Janitor (janitor)]

[Expired for unity-control-center (Ubuntu) because there has been no activity for 60 days.]

[Gunnar Hjalmarsson (gunnarhj)]

Re-opening, since the question was answered properly.