Unbale to add Exchange 2007 UM role

Hi,

I'm trying to add UM role on an existing exchange 2007 sp3 server running on Windows 2008 SP2.
Desktop-Experience is already installed ! and i get the following error ::

"This computer requires Windows Media Audio Voice Codec. Install the Desktop
-Experience component via Server Manager"

Any idea ?
DV

-------------------

exsetup /m:install /r:UM

Welcome to Microsoft Exchange Server 2007 Unattended Setup
The following server roles will be installed
    Unified Messaging Server Role

Performing Microsoft Exchange Server Prerequisite Check

    Unified Messaging Role Checks    ......................... FAILED
     This computer requires Windows Media Encoder. Install the Desktop-Experienc
e component via Server Manager.

     This computer requires Windows Media Audio Voice Codec. Install the Desktop
-Experience component via Server Manager.

The Exchange Server Setup operation did not complete. For more information, visi
t http://support.microsoft.com and enter the Error ID.