$$('a.error').addEvent('mouseover', function(event){
  $('error_box').innerHTML = '<img class="pngfix" src="/img/cross.png"/> ' + this.firstChild.alt;
  $('error_box').style.display = 'block';
  if (event.pageY) {
    var top = event.pageY;
  } else if (event.clientY) {
    var top = event.clientY;
  }
  $('error_box').style.top = top + 'px';
  $('error_box').style.left = '370px';
});

$$('a.error').addEvent('mousemove', function(event){
  if (event.pageY) {
    var top = event.pageY;
  } else if (event.clientY) {
    var top = event.clientY;
  }
  $('error_box').style.top = top + 'px';
  $('error_box').style.left = '370px';
});

$$('a.error').addEvent('mouseout', function(event){
  $('error_box').style.display = 'none';
});