It looks like you have something like the following in your theme:
[code:2o20u2ox] <div id="menu">
<ul>
<?php pixopoint_menu(); ?>
</ul>
</div>
[/code:2o20u2ox]
Try changing it to just this:
[code:2o20u2ox]<?php pixopoint_menu(); ?>[/code:2o20u2ox]
You can’t wrap the plugin function with a UL tag as it will create invalid code.