Why can't I use res.redirect twice?

  create: function(req, res, next) {

    // Check for email and password in params sent via the form, if none
    // redirect the browser back to the sign-in form.
    console.log(req.param('name'));


    if (!req.param('email') || !req.param('password')) {
                var usernamePasswordRequiredError = [{
                    name: 'usernamePasswordRequired',
                    message: 'You must enter both a username and password.'
                }]

                // Remember that err is the object being passed down (a.k.a. flash.err), whose value is another object with
                // the key of usernamePasswordRequiredError
                req.session.flash = {
                    err: usernamePasswordRequiredError
                }

                res.redirect('/session/new');
                return;

    }

    User.findOne({name:req.param('name'),encryptedPassword:req.param('encryptedPassword')}).exec(function foundUser(err, user) {

            if (!user) return next(new Error('User not found.'));



                console.log("auth  this user");

                // Log user in
                req.session.authenticated = true;
                req.session.User = user;

                res.redirect('/user/show/'+user.id);



    });

}

In this code res.redirect won't work. It will if I comment the first one. I got an error, searched for it and found out this was the issue but I don't understand why I can't do that? I'm learning sails with sailscast and the guy seems to do that a lot. See here: http://ift.tt/1JMfPni my code is based on this