Error in mongodb...

//with the following index...
  db.listings.ensureIndex({'_meta.sort_date':-1,listing_id:-1});

//GIVEN THE FOLLOWING INPUTS...
  var sort= [["_meta.sort_date",-1],["_meta.listing_id",-1]];
  var find= {"listing_status":"active"};
  var fields = {
    "listing_id":true,"_meta.sort_date":true,"_meta.vyear":true,"_meta.vmake":true
    ,"_meta.vmodel":true,"_meta.vpkg":true,"contact":true,"tags":true
    ,"vehicle.vin":true,"vehicle.mfg_make":true,"vehicle.mfg_model":true
    ,"vehicle.mfg_year":true,"vehicle.mfg_package":true,"vehicle.images.url_thumb":true
    ,"desc_html":true,"price":true,"is_obo":true,"_id":false
  };
  var sort = [["_meta.sort_date",-1],["_meta.listing_id",-1]];
  var skip = 20420;
  var limit = 10;

//I run the following
  db.listings.find(find,fields).sort(sort).limit(limit).skip(skip);

//At the mongodb console, no problem, runs fine...

//via Node's adapter, I get the following error...
"too much data for sort() with no index.  add an index or specify a smaller limit"