TypeError: Object #<IncomingMessage> has no method 'flash'

I'm getting the following error while using Node.js and Express. Here are my versions :

Node : v0.8.8
Express: 3.0.0rc3

The following error is obtained while trying to access the page :

TypeError: Object #<IncomingMessage> has no method 'flash'
    at routes (/Users/nblavoie/Desktop/HotPie/HotPie/apps/authentication/routes.js:23:8)

I've tried to remove the app.use(app.router); from the app.js with no success. Here is the code that causes the error. See req.flash line.

app.post('/sessions', function(req, res)
{
    if(req.body.user == 'piechief' 
        && req.body.password == '12345')
    {
        req.session.currentUser = req.body.user;
        req.flash('info', "You're logged in as #{req.session.currentUser}");
        res.redirect("/login");
        return;
    }
    else
    {
        req.flash('error', "Those credentials were incorrect. Try again.");
        res.redirect("/login");
        return;
    }
});

Here is the interesting part of my app.js :

var app = express();

app.configure(function(){
  app.set('port', process.env.PORT || 3000);
  app.set('views', __dirname + '/views');
  app.set('view engine', 'jade');
  app.use(express.favicon());
  app.use(express.logger('dev'));
  app.use(express.bodyParser());
  app.use(express.methodOverride());
  app.use(express.cookieParser());
  app.use(express.session({
    secret: "DBBD6BE563419EDB0E5CBD228E603D4AD232CE05434B4FA95C6908B64EA515C3",
    store: new RedisStore({
      host: "127.0.0.1",
      port: "6379",
      db: "mydb"
    })
  }));
  app.use(app.router);
  app.use(express.static(path.join(__dirname, '/public')));
});

Any idea please? I've took a loof at the Express'flash documentation and I can't see what I'm doing wrong.