Thanks Brian, here are the related config files:
vars.xml

  <X-PRE-PROCESS cmd="set" data="hold_music_conf=local_stream://mp3"/>

moduels.conf.xml

   <!-- File Format Interfaces -->
    <load module="mod_sndfile"/>
    <load module="mod_native_file"/>
    <!--For icecast/mp3 streams/files-->
   <load module="mod_shout"/>
    <!--For local streams (play all the files in a directory)-->
    <load module="mod_local_stream"/>
    <load module="mod_tone_stream"/>

local_strean.conf.xml:

<directory name="mp3" path="$${base_dir}/sounds/music/mp3">
    <param name="rate" value="8000"/>
    <param name="shuffle" value="true"/>
    <param name="channels" value="1"/>
    <param name="interval" value="20"/>
    <param name="timer_name" value="soft"/>
  </directory>

and all MP3 files are placed under /opt/local/freeswitch/sounds/music/mp3

It had been working fine until recently (a couple of days or weeks ago, when mod_shout undergone some changes I guess)

Am I missing some new settings?

Thanks,

Chris