I had a simple rollover effect for menu items in wordpress that was working fine and recently quit, any ideas?

 

<script type="text/javascript">
$(document).ready(function() {
$("img.rollover").hover(
function() { this.src = this.src.replace("_off", "_on");
},
function() { this.src = this.src.replace("_on", "_off");
});
});
</script>

<a href="about/">
 <img src="<?php bloginfo('template_url'); ?>/fw_images/about_off.png" class="rollover" /></a>

 

Steve