function validateUpgrade(form, nMUOption) {

  var upgradeCheckbox = -1;
  var checkUpgrade = true;

  if (nMUOption == "Y" ) {

    for (var i = 0; i < form.length; i++) {
      var elem = form.elements[i];
  
      if (elem.name == "MUUpgrade" && elem.type == "checkbox" ) {
        upgradeCheckbox = i;
      }

      if (elem.name == "fareBundle") {
        if (elem.value == "B5-Coach" || elem.value == "B4-Coach" || elem.value == "B3-Coach" ) {
          checkUpgrade = true; 
        } else {
          checkUpgrade = false; 
        }
      } // end if
    } // end for
  
    if (upgradeCheckbox >= 0){
      if ( checkUpgrade == false) {
        form.elements[upgradeCheckbox].checked = false;
	form.elements[upgradeCheckbox].disabled = true;
      } else {
        form.elements[upgradeCheckbox].disabled = false;
	form.elements[upgradeCheckbox].checked = true;
      }
    } 

  } // end if (nMUOption == "Y" )

  return true;

}