You appear to be using the old "Ryans Suckerfish Menu plugin". That does exactly the same thing as the PixoPoint Menu plugin which you already have installed, minus a bunch of other stuff (like adding a menu to your site).
There’s a bunch of nonsensical looking code in your pages which I assume is causing the problem you are experiencing:
[code:84jd41g3]<div id="top-menu">
<ul><ul>
</ul> [/code:84jd41g3]
Try removing that (and their corresponding closing tags if they exist) and hopefully your problem will go away.