toggleMenu not defined error in Magento

I have run into this error after an upgrade to magento 1.4.1.1

toggleMenu not defined.

This is a Javascript error and is to my suprise why it’s there in the first place!

Anyway, here is a temporary solution hoping Magento will one day decide to fix it!

Navigate to pp/code/core/Mage/Catalog/Block/Navigation.php file

Around line 246: replace

$attributes['onmouseover'] = 'toggleMenu(this,1)';
$attributes['onmouseout'] = 'toggleMenu(this,0)';

with

$attributes['onmouseover'] = 'Element.addClassName(this, \'over\')';
$attributes['onmouseout'] = 'Element.removeClassName(this, \'over\')';

Drop a line if you have any cleaner solution!

NOTE:
They say practice makes it perfect! Instead of editing your core files as above please use the approach below as its a lot more cleaner than the one above:
You can add this Javascript code in one of your javascript files that are used across the site.

function toggleMenu(el, over)
{
    if (over) {
        Element.addClassName(el, 'over');
    }
    else {
        Element.removeClassName(el, 'over');
    }
}