Script : how to copy xmpDM:logComment into DC:Description ?

Hi !

I'm fiddling with this code to copy the xmpDM:logComment field into the DC:Description field and each time i run it, it fails saying an error relating to : Unregistred Namespace.

Code comes from here : http://forums.adobe.com/message/3847726

#target bridge   
 if( BridgeTalk.appName == "bridge" ) {  
descToTitle = MenuElement.create("command", "Log Comment to Description", "at the end of Tools");
}
descToTitle.onSelect = function () { 
 if (ExternalObject.AdobeXMPScript == undefined) ExternalObject.AdobeXMPScript = new ExternalObject("lib:AdobeXMPScript");
 var thumb = app.document.selections;
    for(var s in thumb){
 if(thumb.hasMetadata){
        var selectedFile = thumb.spec;
  var myXmpFile = new XMPFile( selectedFile.fsName, XMPConst.UNKNOWN, XMPConst.OPEN_FOR_UPDATE);
  var myXmp = myXmpFile.getXMP();
         var LogComment = getProperty.(XMPConst.NS_DM, "logComment"); 
        myXmp.deleteProperty(XMPConst.NS_DC, "description");
        myXmp.appendArrayItem(XMPConst.NS_DC, "description", LogComment, 0, XMPConst.ALIAS_TO_ALT_TEXT);
        myXmp.setQualifier(XMPConst.NS_DC, "description[1]", "http://www.w3.org/XML/1998/namespace", "lang", "x-default");
    }
function getArrayItems(ns, prop){
var arrItem=[];
try{
var items = myXmp.countArrayItems(ns, prop);
 for(var i = 1;i <= items;i++){
 arrItem.push(myXmp.getArrayItem(ns, prop, i));
     }
return arrItem;
}catch(e){alert(e +" Line: "+ e.line);}
}
        if (myXmpFile.canPutXMP(myXmp)) { 
        myXmpFile.putXMP(myXmp);
        myXmpFile.closeFile(XMPConst.CLOSE_UPDATE_SAFELY); 
         } else {
  xmpFile.closeFile();
        }
    }
}

Can anyone point me where my error is ?

thx!