Error uploading image (in bytes) to a HTTP File server

I am trying to upload an image (in bytes) from a HTTP server. I am encountering an error "An existing connection was forcibly closed by the remote host" when using the code below. DownloadData and UploadFile methods are working. Please help.

string image = @"C:\.....\helloX2.pdf";

byte[] ImageData = System.IO.File.ReadAllBytes(image);

Uri _uri = new Uri(@"http://XXX.XXX.XX.X:8080/MyHTTPFileServer/helloX2.pdf");

WebClient client = new WebClient();

client.Credentials = CredentialCache.DefaultCredentials;

byte[] responseArray = client.UploadData(_uri, "POST",ImageData);

string x = Encoding.ASCII.GetString(responseArray);

client.Dispose();