express：node throwing error on mongodb

1: C:\Node_app\microblog\node_modules\connect-mongo\lib\connect-mongo.js:126

'Error connecting to database');

   3:               ^

   4: Error: Error connecting to database

   5:     at module.exports.MongoStore.__proto__ (C:\Node_app\microblog\node_module

   6:     at Db.open (C:\Node_app\microblog\node_modules\connect-mongo\node_modules

   7:     at Server.connect.connectionPool.on.server._serverState (C:\Node_app\micr

   8: ion\server.js:408:7)

   9:     at EventEmitter.emit (events.js:115:20)

  10:     at connection.on.connectionStatus (C:\Node_app\microblog\node_modules\con

  11: :93:15)

  12:     at EventEmitter.emit (events.js:91:17)

  13:     at Socket.errorHandler (C:\Node_app\microblog\node_modules\connect-mongo\

  14:     at Socket.EventEmitter.emit (events.js:88:17)

  15:     at Socket._destroy.self.errorEmitted (net.js:329:14)

  16:     at process.startup.processNextTick.process._tickCallback (node.js:244:9)