Jquery :: Uncaught TypeError - Cannot Call Method Of Null

I have a jQuery script which works fine online, but when it comes to testing locally I get this error on the 2nd line of code:
Uncaught TypeError: Cannot call method 'hide' of null
So, that means I'm trying to call a method on something that doesn't exist, or is set to null. But I'm trying to call the method on anything with the class menu. And there are divs with the class menu on my page. The script runs fine on several other pages, so it must have something to do with this page in particular, but I have no idea why...

Here's my HTML:
Code:
<div id="navigation">
<ul id="navbar">
<li><a href="[URL]">Home</a></li>
<li><a class="drop-down" href="#">Food Menu</a></li>
<li><a class="drop-down" href="#">Drinks Menu</a></li>
<li><a href="gallery.html.php">Gallery</a></li>
<li><a href="function.html.php">Function Room</a></li>
<li><a href="contact.php">Contact Us</a></li>
</ul>
<div id="drinks" class="menu"> .....

And my jQuery script:
Code:
$(document).ready(function(){
$('.menu').hide();
$('a, #header').not('.drop-down, .menu a').hover(function(){
$('.menu').hide();
});
$('.drop-down').mouseenter(function(){
$('.menu').hide();
id=($(this).text().toLowerCase().replace(' menu', ''));
$('#' + id).show();
});
$('.menu').mouseleave(function(){
$('.menu').hide();
});});

I've put up the page online, but I don't have a direct link to it because it's a live site. You can see the code working here: The Pilot, and the offending page is here: The Gallery.