unable to find mp3encoder

[yves]

when trying to setup mp3encoder in rhythmbox
i get :

"Impossible de trouver le greffon requis
Python (v2.7) nécessite d'installer des greffons pour créer des fichiers multimédia du type suivant : Codeur MPEG-1 Layer 3 (MP3)"

and on the terminal

(rhythmbox:4378): GLib-GObject-CRITICAL **: g_object_unref: assertion `G_IS_OBJECT (object)' failed
Rhythmbox-Message: Missing plugin: gstreamer|0.10|rhythmbox|Codeur MPEG-1 Layer 3 (MP3)|encoder-audio/mpeg, mpegversion=(int)1, layer=(int)3
/usr/lib/python2.7/dist-packages/gobject/constants.py:24: Warning: g_boxed_type_register_static: assertion `g_type_from_name (name) == 0' failed

but ihave the missing encoder:

~$ gst-inspect lamemp3enc
Factory Details:
  Long name: L.A.M.E. mp3 encoder
  Class: Codec/Encoder/Audio
  Description: High-quality free MP3 encoder
  Author(s): Sebastian Dröge <email address hidden>
  Rank: primary (256)

Plugin Details:
  Name: lame
  Description: Encode MP3s with LAME
  Filename: /usr/lib/x86_64-linux-gnu/gstreamer-0.10/libgstlame.so
  Version: 0.10.19
  License: LGPL
  Source module: gst-plugins-ugly
  Source release date: 2012-02-20
  Binary package: GStreamer Ugly Plugins (Ubuntu)
  Origin URL: https://launchpad.net/distros/ubuntu/+source/gst-plugins-ugly0.10

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.