Backbone.js model.save() - proper server response
===

Something seems to be wrong, either my server response or my save function.
In neither case success nor error function of model.save() gets invoked.

My server response:

    exports.updateBusinessBannerAd = function(req, res) {
    // update banner ad
    db.insert(req.body, req.body._id, function(err, data) {
        if (err) {
            console.log('Update business banner ad: ' + err.message + '   ' + err['status-code']);
            res.send(err['status-code'], { header: 'Update banner ad', message: err.message, type: 'error'});
        }
        else {
            res.send(200);
        }
    }); 
};

And here my client code:

    saveBannerAd: function(self) {
            self.model.id = self.model.attributes._id; 
            self.model.save({
                success: function(model, res) {
                        utils.growl( 'Banner Ad', 'has been updated!', 'info');
                        self.resetHandler();
                },
                error: function(model, res) {
                    console.log(res);
                    utils.growl(res.header, res.message, res.type);
                    return;
                }    
            }); 
        },


What am I missing?