// Checking for mandatory fields
YAHOO.util.Event.onDOMReady( function(){
  var form = YAHOO.util.Dom.get( 'course_search' );
  YAHOO.util.Event.addListener( form, 'submit',checkForm);
});

function checkForm(e)
{
      if ( this.searchStudyFieldID.value == "" ||
           this['searchStateCodes[]'].value == "" )
      {
        YAHOO.util.Event.stopEvent(e);
        alert("Both Study Field and Location must be selected");
      }
}