can not play audio/video files and cannot install plugins

GLib-CRITICAL **: g_once_init_leave: assertion `initialization_value != 0' failed

Order of messages:

Search for suitable plugin?
The required software to play this file is not installed. You need to install suitable plugins to play media files. Do you want to search for a plugin that supports the selected file?

The search will also include software which is not officially supported.

Cancel/ Search - selected Search option

Packages available are shown and when I click install(and after authenticating) a message will come
Requires installation of untrusted packages
The action would require the installation of packages from not authenticated sources.

No packages installed
None of the selected packages were installed.

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: libgstreamer0.10-0 0.10.30-1build2
ProcVersionSignature: Ubuntu 2.6.35-22.33-generic 2.6.35.4
Uname: Linux 2.6.35-22-generic i686
Architecture: i386
Date: Sat Mar 19 14:08:58 2011
ExecutablePath: /usr/bin/totem
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Release i386 (20101007)
ProcEnviron:
 LANG=en_IN
 SHELL=/bin/bash
SourcePackage: gstreamer0.10
XsessionErrors:
 (polkit-gnome-authentication-agent-1:1355): GLib-CRITICAL **: g_once_init_leave: assertion `initialization_value != 0' failed
 (nautilus:1346): GConf-CRITICAL **: gconf_value_free: assertion `value != NULL' failed
 (nm-applet:1351): Gdk-CRITICAL **: IA__gdk_window_thaw_toplevel_updates_libgtk_only: assertion `private->update_and_descendants_freeze_count > 0' failed