Empty body, SyntaxError: Unexpected token:

I am getting

Authenticating client with key "d4cf701036e875bc1721c7df56334135"
Sending message to backend { authToken: 'd4cf701036e875bc1721c7df56334135',
messageType: 'authenticate',
clientId: 'Er8IMWGkkt3mV5GHAAAA' } { uri: 'http://d7.local:80//nodejs/message',
body: 'messageJson=%7B%22authToken%22%3A%22d4cf701036e875bc1721c7df56334135%22%2C%22messageType%22%3A%22authenticate%22%2C%22clientId%22%3A%22Er8IMWGkkt3mV5GHAAAA%22%7D&serviceKey=',
headers:
{ 'Content-Length': 173,
'Content-Type': 'application/x-www-form-urlencoded' } }
Failed to parse authentication message: [SyntaxError: Unexpected token ]
Failed message string: 

// my config.js is

settings = {
  host:'d7.local',
  port:8888,
  resource:'/socket.io',
  serviceKey:'', /* 'invalid key error' even If I set same key on nodejs and drupal */
  backend: {
    port: 80,
    host: 'd7.local',
    messagePath: '/nodejs/message'
  },
  debug: true,
  extensions: [],
  transports: ['websocket', 'polling']
};

on authenticate, drupal returns auth_user object, but in nodejs server.js, the 'body' key of response object was Empty!

on '/nodejs/message' path on server, it gives '{"error":"Invalid service key."}'. So there is no other module doing redirect or something.

I have authcache installed, but nodejs* path is excluded from caching.
Cache cleared.

What could be wrong? help me to debug it.

Nodejs v0.10.25
Ubuntu 14.04
Php 5.4
Drupal 7.29
Nginx 1.4.6