What is 904 Transaction Ended Response for HTTP Request

I have a AngularJS web application. My server runs with Java/Spring. I have a login page in UI that takes user name and password. I run the application on AWS EC2 with HTTPS. When I test the application manually through broswer, I'm able to send request to my server from UI and get proper response. However, when I'm using a selenium script to monitor the application, I got a 904 Transaction Ended. What does this mean ? Following is the request and response message from logs.

{  
            "time":743,
            "request":{  
               "method":"POST",
               "headers":[  
                  {  
                     "name":"Accept-Language",
                     "value":"en-US,en;q=0.5"
                  },
                  {  
                     "name":"accountId",
                     "value":"121232131"
                  },
                  {  
                     "name":"Host",
                     "value":"aws.hostname.com"
                  },
                  {  
                     "name":"Content-Length",
                     "value":"57"
                  },
                  {  
                     "name":"Referer",
                     "value":"http://ift.tt/1Eejy8F"
                  },
                  {  
                     "name":"Accept-Encoding",
                     "value":"gzip, deflate"
                  },
                  {  
                     "name":"User-Agent",
                     "value":"Mozilla/5.0 (Windows NT 6.0; rv:31.0; Neustar WPM) Gecko/20100101 Firefox/31.0"
                  },
                  {  
                     "name":"Content-Type",
                     "value":"application/x-www-form-urlencoded; charset=UTF-8"
                  },
                  {  
                     "name":"Connection",
                     "value":"keep-alive"
                  },
                  {  
                     "name":"Accept",
                     "value":"application/json, text/plain, */*"
                  },
                  {  
                     "name":"Cache-Control",
                     "value":"no-cache"
                  },
                  {  
                     "name":"Pragma",
                     "value":"no-cache"
                  }
               ],
               "url":"http://ift.tt/1vPPCZx",
               "queryString":[  

               ],
               "cookies":[  

               ],
               "httpVersion":"HTTP/1.1",
               "bodySize":-1,
               "postData":{  
                  "params":[  
                     {  
                        "name":"username",
                        "value":"user@stackoverflow.com"
                     },
                     {  
                        "name":"password",
                        "value":"confused"
                     }
                  ],
                  "text":"username=user%40stackoverflow.com&password=confused",
                  "mimeType":"application/x-www-form-urlencoded; charset=UTF-8"
               },
               "headersSize":12
            },
            "response":{  
               "content":{  
                  "size":0
               },
               "headers":[  

               ],
               "status":904,
               "cookies":[  

               ],
               "statusText":"Transaction ended",
               "httpVersion":"HTTP/1.1",
               "bodySize":0,
               "redirectURL":"",
               "headersSize":0
            },
            "pageref":"2",
            "startedDateTime":"2015-02-20T20:29:14.390+0000",
            "cache":{  

            },
            "timings":{  
               "blocked":-1,
               "dns":-1,
               "connect":-1,
               "send":0,
               "wait":0,
               "receive":743,
               "ssl":-1
            },
            "_wsid":0
         }