update-manager won't launch either automatically or manually

Since some time (sorry, don't noticed exactly which update resulted in that behavior...), Update Manager won't launch automatically nor manually.

When launched manually from CLI, I get this error every time :
user@system:~$ sudo update-manager
Traceback (most recent call last):
  File "/usr/bin/update-manager", line 28, in <module>
    from gi.repository import Gtk
EOFError: EOF read where not expected

When launched from Unity menu, it happens just nothing....

Regards

ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: update-manager 1:0.174.3
Uname: Linux 3.5.0-21-generic x86_64
Architecture: amd64
Date: Tue Dec 25 19:12:07 2012
MarkForUpload: True
PackageArchitecture: all
SourcePackage: update-manager