function btnOK_onclick() {
 if (document.Formular.upfile.value == "") {
  alert('Please select a file for upload.');
  window.location.reload();
 }
 var filename = document.Formular.upfile.value;
 var pregmatch = filename.match(/\.(mp3)/);
 if(pregmatch) {
  alert("The file type you are trying to upload is not allowed.");
  window.location.reload();
 }
}