title: MongoError: Incorrect arguments
body: <p>Suddenly got this error in my log-in function and I can't figure out exactly what is causing it. I checked both cases where I use query or insert into MongoDB, but can't see any problems with the arguments. Just using json in the first argument, and a callback function in the second, which I think should work and seems to work in other cases where I use it. I think I may have syntax error(maybe) or something that might be causing it. Any ideas?<br>
  First Mongo usage:</p>
  
  <pre><code>this.validateLogin = function(username, password, callback){
      "use strict";
      users.findOne({'_id' :username }, function (err,user){
          //some code
      });
  }
  </code></pre>
  
  <p>Second Mongo usage:</p>
  
  <pre><code>sessions.insert(session, function (err, result) {
          "use strict";
          callback(err, session_id);
      });
  </code></pre>
  
  <p>Here is the Error:</p>
  
  <pre><code>C:\...\node_modules\mongodb\lib\mongodb\connection\b
  ase.js:242
          throw message;
                ^
  MongoError: Incorrect arguments
      at Object.toError (C:\...\node_modules\mongodb\l
  ib\mongodb\utils.js:110:11)
      at Server.Base._callHandler (C:\...\node_modules
  \mongodb\lib\mongodb\connection\base.js:444:65)
      at C:\...\node_modules\mongodb\lib\mongodb\conne
  ction\server.js:485:18
      at MongoReply.parseBody (C:\...\node_modules\mon
  godb\lib\mongodb\responses\mongo_reply.js:68:5)
      at null.&lt;anonymous&gt; (C:\...\node_modules\mongodb
  \lib\mongodb\connection\server.js:443:20)
      at EventEmitter.emit (events.js:95:17)
      at null.&lt;anonymous&gt; (C:\...\node_modules\mongodb
  \lib\mongodb\connection\connection_pool.js:191:13)
      at EventEmitter.emit (events.js:98:17)
      at Socket.&lt;anonymous&gt; (C:\...\node_modules\mongo
  db\lib\mongodb\connection\connection.js:418:22)
      at Socket.EventEmitter.emit (events.js:95:17)
  </code></pre>
  
  <p>Thanks in advance!</p>