{"The remote server returned an error: (400) Bad Request."} why?

private string FileManagerServiceUrl
      {
          get
          {
              return "http://localhost/FileSync.SyncService/TransferService.svc";
          }
      }

string requestFile = @"D:\TestFolder\item.zip";
           string fileSavePath = @"D:\TestFolder\copyContainer\testfile.zip";
           DownLoadFileFromRemoteLocation(requestFile, fileSavePath);

private void DownLoadFileFromRemoteLocation(string downloadFileLocation, string downloadedFileSaveLocation)
      {
          string serviceUrl = string.Format("{0}/RetrieveFile/{1}", FileManagerServiceUrl, downloadFileLocation);
          var request = WebRequest.Create(serviceUrl);
          request.UseDefaultCredentials = true;
          request.PreAuthenticate = true;
          request.Credentials = CredentialCache.DefaultCredentials;
          using (var response = request.GetResponse())
          {
              using (var fileStream = response.GetResponseStream())
              {
                  CreateDirectoryForSaveLocation(downloadedFileSaveLocation);
                  SaveFile(downloadedFileSaveLocation, fileStream);
              }
          }


      }

public Stream RetrieveFile(string path)
      {
          if (WebOperationContext.Current == null) throw new Exception("WebOperationContext not set");

          // As the current service is being used by a windows client, there is no browser interactivity.
          // In case you are using the code Web, please use the appropriate content type.
          var fileName = Path.GetFileName(path);
          WebOperationContext.Current.OutgoingResponse.ContentType = "application/octet-stream";
          WebOperationContext.Current.OutgoingResponse.Headers.Add("content-disposition", "inline; filename=" + fileName);

          return File.OpenRead(path);
      }