Sound button

I have an ambient sound in my pano that starts "onloaded". I wish to create a button to mute or to turn on the sound once again. here is my code that doesn't work. Can you tell me what's wrong in this script?

hub

<plugin name="soundinterface"
url="../../plugins/soundinterface.swf"
rootpath="sound"
onloaded="action(play)"
/>

<action name="play">
playsound(sound,depart.mp3,loops = 0);
</action>

<plugin name="btn_speaker_off" url="../../buttons/btn_speaker_off.png" visible="true" align="rightbottom" edge="rightbottom" y="10" x="110" alpha="0.7" onhover="showtext(couper son)" onover="set(alpha,1.0)" onout="set(alpha,0.7)"
onclick="action(mute); set(plugin[sound_off].visible,false); set(plugin[sound_on].visible,true)"/>
<plugin name="btn_speaker_on" url="../../buttons/btn_speaker_on.png" visible="false" align="rightbottom" edge="rightbottom" y="10" x="110" alpha="0.7" onhover="showtext(brancher son)" onover="set(alpha,1.0)" onout="set(alpha,0.7)"
onclick="action(play); set(plugin[sound_on].visible,false); set(plugin[sound_off].visible,true)"/>

<action name="mute">
stopsound(sound,depart.mp3)
</action>

Thank you! It works now.
May you explain me why it works with "soundinterface", but not with the "sound"? What is the difference beetween these plugins?

<plugin name="soundinterface"
url="../../plugins/soundinterface.swf"
onloaded="action(play)"
/>

<plugin name="btn_speaker_on" url="../../buttons/btn_speaker_on.png" visible="false" align="rightbottom" edge="rightbottom" y="10" x="110" alpha="0.7" onhover="showtext(brancher son)" onover="set(alpha,1.0)" onout="set(alpha,0.7)"
onclick="action(play) "/>

<plugin name="btn_speaker_off" url="../../buttons/btn_speaker_off.png" visible="true" align="rightbottom" edge="rightbottom" y="10" x="110" alpha="0.7" onhover="showtext(couper son)" onover="set(alpha,1.0)" onout="set(alpha,0.7)"
onclick="action(mute) "/>

<action name="play">
playsound(sound,sound/depart.mp3); set(plugin[btn_speaker_on].visible,false); set(plugin[btn_speaker_off].visible,true);
</action>

<action name="mute">
stopsound(sound); set(plugin[btn_speaker_off].visible,false); set(plugin[btn_speaker_on].visible,true);
</action>