Error with schema, model and controller (mongoose)

I'm developing an app with node.js, mongodb, mongoose and I get an error when I added these files.

This is the "model.js" file:

var mongoose = require('mongoose'),
  Schema = mongoose.Schema;

var RequestDiffSchema = new Schema({
  id: {
    type: Number,
    unique: true,
    required:true
  },
  solicitudId: { 
    type: Number,
    required: true
  },
  errors: { 
    type: String,
    required:true
  }
}, { collection: 'requestdiff' });

module.exports = mongoose.model('RequestDiff', RequestDiffSchema);

And this is the "controller.js" file:

'use strict';

var mongoose = require('mongoose'),
    RequestDiff = mongoose.model('RequestDiff'),
    q = require('q'),
    Promise = q.Promise;


var RequestDiffController = {


  // Aquí van las funciones


};

module.exports = RequestDiffController;

I get an error when I raise the server and I can not fix it, did something wrong? some mistake? or am I missing a step?

The error that throws me by console is:

Error initializing middleware
MissingSchemaError: Schema hasn't been registered for model "RequestDiff".
Use mongoose.model(name, schema)
    at Mongoose.model (/Documentos/api/backend.server/node_modules/mongoose/lib/index.js:349:13)
    at Object.<anonymous> (Documentos/api/backend.server/api/controllers/requests-diff.js:7:28)
    at Module._compile (module.js:570:32)
    at Object.Module._extensions..js (module.js:579:10)

Is it because the model does not take me well? The routes are correct and I do not see the fault ...