Geo spatial index in mongodb with node.js

I am finding problem in defining the geo spatial index '2d' as shown below. Any clue as to what is going wrong ?

var Address = new Schema({
      loc           : {lat: Number,  lng: Number },
      Address       : String,
      create_date       : {type: Date, default: Date.now}
});
Address.index ({
       loc : "2d"
});

It throws error like,

events.js:45 throw arguments[1]; // Unhandled 'error' event ^ Error: point not in range at [object Object]. (/cygdrive/c/Personal/software/ nodejs/NODE/no de_modules/mongoose/node_modules/mongodb/lib/mongodb/db.js:503:20)

EDIT: added the code

var Address = new Schema({
      type              : {type: String, enum: ['Apartment', 'House', 'Serviced Apartment'], default: 'Apartment'}, 
      loc               : {lat: Number,  lng: Number },
      Address           : String,
      create_date       : {type: Date, default: Date.now}
});

/*
Address.index ({
    loc : "2d"
});
*/

mongoose.connect('mongodb://127.0.0.1:27017/test123', function(err) {
    if (err) {
        console.log("error in mongo connection");
        throw err;
    }
    console.log("connected to mongo");
});

var RentModel = mongoose.model('Rent', Address);



socket = io.listen(app);

socket.sockets.on('connection', function(client){ 

        console.log('inside on connection');

        client.on('register', function(msg){ 
                console.log("msg.geometry.type", msg.geometry.type);

                var rent = new RentModel();
                rent.type = 'Apartment';
                rent.loc.lat = 23;
                rent.loc.lng = 56;
                rent.Address = "LLLLLLLLIIIIIIIOOOOOOONNNNNNNN"

                console.log("before save");
                rent.save(function(err){
                    console.log("rent.save start");
                    if(err) {