Depois que faço o cadastro pela view da esse erro

be-mean.md

Conectado.
Conexão aberta.
Produto criado:  { products: 
   { __v: 0,
     price: 100,
     _id: 54d91be6ef55d769c45bc4f0,
     created_at: Mon Feb 09 2015 18:43:18 GMT-0200 (BRST),
     description: 'Gente boa',
     name: 'Gravino' } }
POST /api/products 200 37.995 ms - 137

/Users/fernandoguisso/Desktop/be-mean/node/express/node_modules/mongoose/lib/utils.js:413
        throw err;
              ^
Error: Can't set headers after they are sent.
    at ServerResponse.OutgoingMessage.setHeader (http.js:689:11)
    at ServerResponse.header (/Users/fernandoguisso/Desktop/be-mean/node/express/node_modules/express/lib/response.js:695:10)
    at ServerResponse.send (/Users/fernandoguisso/Desktop/be-mean/node/express/node_modules/express/lib/response.js:146:12)
    at ServerResponse.json (/Users/fernandoguisso/Desktop/be-mean/node/express/node_modules/express/lib/response.js:235:15)
    at Promise.<anonymous> (/Users/fernandoguisso/Desktop/be-mean/node/express/controllers/products.js:11:7)
    at Promise.<anonymous> (/Users/fernandoguisso/Desktop/be-mean/node/express/node_modules/mongoose/node_modules/mpromise/lib/promise.js:177:8)
    at Promise.emit (events.js:98:17)
    at Promise.emit (/Users/fernandoguisso/Desktop/be-mean/node/express/node_modules/mongoose/node_modules/mpromise/lib/promise.js:84:38)
    at Promise.fulfill (/Users/fernandoguisso/Desktop/be-mean/node/express/node_modules/mongoose/node_modules/mpromise/lib/promise.js:97:20)
    at handleSave (/Users/fernandoguisso/Desktop/be-mean/node/express/node_modules/mongoose/lib/model.js:133:13)
9 Feb 18:43:18 - [nodemon] app crashed - waiting for file changes before starting...

express.js

var express = require('express')
  , app = express()
  , path = require('path')
  ;
//renderizar html
app.get('/', function(req, res){
  res.sendFile(path.join(__dirname+'/index.html'));
});
//