KOA POST parsing error

I'm trying to get the POST data using koa-body-parser but I get the following error :

SyntaxError: Unexpected token e
  at Object.parse (native)

This error refer to

/co-body/node_modules/raw-body/index.js

I think that the library co-body is trying to use "parse" but in my node version this function is restricted.

I'm using node 0.11.13

This is a part of the app.js

var path=require('path');
var koa = require('koa');
var app = koa();

app.use(require('koa-body-parser')());

//enrutamiento
app.use(require('./configs/routes')(app));

This is the function that recibe the call:

function *(){
    /*
    var str = 'email=lopezchr%40gmail.com&password=123123';
    console.log(JSON.parse(str));
    */
    var self = this;
    var attributes= this.request.body
    var userModel = this.models.user;
    userModel.create(this.request.body).exec(function(){
        self.body={success:true,description:"user Created"}
    });
}

Aditionally, when I try to do this:

var str = 'email=lopezchr%40gmail.com&password=123123';
console.log(JSON.parse(str));

I optain the same error..

update

In other post, I realized that string is not a JSON.. sooo... that is the problem...

I'm trying to do this:

$.post('/auth',$(form).serialize(),function(data){
                    console.log(data);
                });

And I want to recibe the form data with koa-body-parce...What should I do?