404 error in node.js

I am getting following error when tried to run the node.js application:

Not Found
404

Error: Not Found
    at Layer.app.use.res.render.message [as handle] (C:\node\app\app.js:41:15)
    at trim_prefix (C:\node\app\node_modules\express\lib\router\index.js:240:15)
    at C:\node\app\node_modules\express\lib\router\index.js:208:9
    at Function.proto.process_params (C:\node\app\node_modules\express\lib\router\index.js:269:12)
    at next (C:\node\app\node_modules\express\lib\router\index.js:199:19)
    at next (C:\node\app\node_modules\express\lib\router\index.js:176:38)
    at C:\node\app\node_modules\express\lib\router\index.js:137:5
    at C:\node\app\node_modules\express\lib\router\index.js:250:10
    at next (C:\node\app\node_modules\express\lib\router\index.js:160:14)
    at next (C:\node\app\node_modules\express\lib\router\index.js:176:38)

below is my code which i am using in app.js

var express = require('express');
var path = require('path');
var favicon = require('static-favicon');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');

var mongo = require('mongodb');
var monk = require('monk');
var db = monk('localhost:27017/app');

var routes = require('./routes/index');
var users = require('./routes/users');

var app = express();

// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'jade');

app.use(favicon());
app.use(logger('dev'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded());
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

app.use(function(req,res,next){
    req.db = db;
    next();
});

app.use('/', routes);
app.use('/users', users);

///var express = require('express');
///var router = express.Router();

/// catch 404 and forward to error handler
app.use(function(req, res, next) {
    var err = new Error('Not Found');
    err.status = 404;
    next(err);
});

/// error handlers

// development error handler
// will print stacktrace
if (app.get('env') === 'development') {
    app.use(function(err, req, res, next) {
        res.status(err.status || 500);
        res.render('error', {
            message: err.message,
            error: err
        });
    });
}

// production error handler
// no stacktraces leaked to user
app.use(function(err, req, res, next) {
    res.status(err.status || 500);
    res.render('error', {
        message: err.message,
        error: {}
    });
});


module.exports = app;

can you please let me what is the root cause of the issue and how this can be resolved.

Below is my router too:

var express = require('express');
var router = express.Router();

/* GET home page. */
router.get('/', function(req, res) {
  res.render('index', { title: 'Express' });
}); 

router.get('/helloworld',function(req,res)
{
    res.render('helloworld',{title: 'World of node js' });
});


router.get('/userlist', function(req, res) {
    var db = req.db;
    var collection = db.get('usercollection');
    collection.find({},{},function(e,docs){
        res.render('userlist', {
            "userlist" : docs
        });
    });
});

module.exports = router;