I was trying to access Settings in Update Manager to setup automatic updates. But the Settings Dialog does not pop up. Cannot Access Software Sources from the Ubuntu Software Center>Edit>Software Sources... either. When I try to run software sources from the terminal I get the following error.

$ sudo software-properties-gtk

Traceback (most recent call last):

  File "/usr/bin/software-properties-gtk", line 26, in <module>

    gi.require_version('Gtk', '2.0')

  File "/usr/lib/python2.7/dist-packages/gi/__init__.py", line 46, in require_version

    raise ValueError('Namespace %s not available' % namespace)

ValueError: Namespace Gtk not available

I understand that the package is looking for GTK namespace and requires Gtk version 2.0
Trying to check what version of GTK is installed, I run the following and get

$ apt-cache showpkg libgtk2.0-0 | more

Package: libgtk2.0-0

Versions: 

2.24.4-0ubuntu2 (/var/lib/apt/lists/Ubuntu%2011.04%20%5fNatty%20Narwhal%5f%20-%2

0Release%20i386%20(20110426)_dists_natty_main_binary-i386_Packages) (/var/lib/ap

t/lists/us.archive.ubuntu.com_ubuntu_dists_natty_main_binary-i386_Packages) (/va

r/lib/dpkg/status)

 Description Language: 

                 File: /var/lib/apt/lists/Ubuntu%2011.04%20%5fNatty%20Narwhal%5f

%20-%20Release%20i386%20(20110426)_dists_natty_main_binary-i386_Packages

                  MD5: 3ed10be69b676a812afff2c7fdaa4017

How do I get software sources to run?

Update:

Found a related question here.I have python2.5 installed, but haven't set up a symbolic link to it, and the above log mentions python2.7