Node.JS bug trying to create a chat
===

I'm currently writing a chat application which will run on Heroku. I'm using Node.JS and Socket.IO for this task. It works perfectly when I run it locally but when I deploy it to heroku I get this error :

    app[web.1]: /app/node_modules/socket.io/lib/manager.js:724
    app[web.1]:   rand.writeInt32BE(this.sequenceNumber, 11);
    app[web.1]:        ^
    app[web.1]: TypeError: Object 

Here's the Socket.IO part of the code (the rest is just classic Express code) :


    var socket = require('socket.io');
    var io = socket.listen(app);

    io.configure(function () { 
        io.set("transports", ["xhr-polling"]); 
        io.set("polling duration", 10); 
        });

    var usernames = {}

    io.sockets.on('connection', function (socket) {
        socket.on('adduser', function(username) {
          socket.username = username;
          usernames[username] = username;
          socket.join('room');
          socket.emit('action', username, 'connected');
          socket.broadcast.to('room').emit('action', username, 'connected');
        });
        socket.on('message', function(message) {
          socket.emit('message', socket.username, message);
          socket.broadcast.to('room').emit('message', socket.username, message);
        });
    });

Has anyone got any idea on how to solve this bug ?