Add comment to work item using API

The remote server returned an error: (400) Bad Reques

//set URL

            HttpWebRequest request =

                WebRequest.Create(new Uri("https://192.168.16.14:9443/jazz/oslc/workitems/_LD0j4K2vEd6wr5OgrMF4rQ/rtc_cm:comments")) as HttpWebRequest;



            //authentication 

            request.Referer = this.refererLogIn;

            request.CookieContainer = this.cookieContainer;



            //Request parameters

            request.ContentType = "application/x-oslc-cm-change-request+xml";

            request.Accept = "text/xml";

            request.Method = "POST";



            //Get the XML file to byte

            byte[] bytes;

                        using (FileStream fsSource = new FileStream(@"C:\xmlCommant.xml",

                        FileMode.Open, FileAccess.Read))

            {

                // Read the source file into a byte array.

                bytes = new byte[fsSource.Length];

                int numBytesToRead = (int)fsSource.Length;

                int numBytesRead = 0;

                while (numBytesToRead > 0)

                {

                    // Read may return anything from 0 to numBytesToRead.

                    int n = fsSource.Read(bytes, numBytesRead, numBytesToRead);



                    // Break when the end of the file is reached.

                    if (n == 0)

                        break;



                    numBytesRead += n;

                    numBytesToRead -= n;

                }

            }

            request.ContentLength = bytes.Length;



            //Write to stream

            Stream newStream = request.GetRequestStream();

            newStream.Write(bytes, 0, bytes.Length);

            newStream.Close();

            

            //Error is thrown

            HttpWebResponse response = request.GetResponse() as HttpWebResponse;