error when selecting MPEG layer 3 audio in Rythmbox

[Carla Sella]

After a fresh install of Precise Pangonlin Beta2 (in both english and italian language), if you try to set MPEG Layer 3 audio in prefered fomat under music preferences, you get a button indicating: "install additional software requred to use this fomat"
(to set the preference, I went on rhythmbox edit menu, preferences, music tab, preferred format).
If you click on this button to try to install the additional sotware, instead of intalling the software you get an error message: "required plugin could not be found. .." see attached screenshot.
I expect ubuntu restricted formats to be installed by clicking on this button instead of the error shown in the screenshot.
If you close the error window and install ubuntu restricted extras from software center o via apt-get install and return to rhythmbox preferences you can see that the MPEG Layer 3 audio setting is accepted without any problem.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: rhythmbox 2.96-0ubuntu3
ProcVersionSignature: Ubuntu 3.2.0-20.33-generic 3.2.12
Uname: Linux 3.2.0-20-generic x86_64
ApportVersion: 1.95-0ubuntu1
Architecture: amd64
Date: Sun Apr 15 13:36:35 2012
ExecutablePath: /usr/bin/rhythmbox
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Beta amd64 (20120328)
ProcEnviron:
 SHELL=/bin/bash
 LANGUAGE=en_US:en
 LANG=en_US.UTF-8
SourcePackage: rhythmbox
UpgradeStatus: No upgrade log present (probably fresh install)