xmlhttp = new XMLHttpRequest();
ADOStream=new ActiveXObject("ADODB.Stream");
ADOStream.Type=1;//1=adTypeBinary
ADOStream.Open();
ADOStream.LoadFromFile(FileItem.path);
var binary=ADOStream.Read();
xmlhttp.open("POST","http://www.example.com/upload.php",true);
xmlhttp.onreadystatechange = XHRFinished;
xmlhttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded; charset=UTF-8");
xmlhttp.send(binary); //I get always "invalid argument" here
ADOStream.Close();