[SOLVED]
I have Lightbox usong prototype.js
The order of loading the scripts makes all the difference
1. <script type="text/javascript" src="js/scriptaculous.js?load=effects"></script>
2. <script type='text/javascript' src='/wp-includes/js/jquery/jquery.js?ver=1.2.6'></script>
3. <script type="text/javascript" src="js/prototype.js"></script>[/code]
And it works perfectly.