probabilmente il problema è nel file html

codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<link href="style.css" rel="stylesheet" type="text/css" />

<script src="js/jquery.js" type="text/javascript" charset="utf-8"></script>
<link href="css/prettyGallery.css" rel="stylesheet" type="text/css" />
<script src="js/jquery.prettyGallery.js" type="text/javascript" charset="utf-8"></script>
<script type="text/javascript" charset="utf-8">
    jQuery(document).ready(function(){
        jQuery("ul.gallery").prettyGallery({
            itemsPerPage : 1,
            animationSpeed : 'normal', /* fast/normal/slow */
            navigation : 'top',  /* top/bottom/both */
            of_label: ' ', /* The content in the page "1 of 2" */
            previous_title_label: 'Previous page', /* The title of the previous link */
            next_title_label: 'Next page', /* The title of the next link */
            previous_label: 'Previous', /* The content of the previous link */
            next_label: 'Next' /* The content of the next link */
        });
    });
</script>


<style type="text/css">
ul.gallery li.none { display:none;}
ul.gallery { margin:35px 24px 0 19px;}
</style>

<style type="text/css">
body { background:#FFF url(images/bg.gif) repeat-x;}
</style>

</head>
<body>
     
          <ul class="gallery">[*][img]images/screen_1.jpg[/img]
            <li class="none">[img]images/screen_2.jpg[/img]
            <li class="none">[img]images/screen_3.jpg[/img][/list]
 
</body>
</html>