SO Answer /My script works in jsfiddle but not site. Cannot call method hover of null?

http://stackoverflow.com/questions/12293505/my-script-works-in-jsfiddle-but-not-site-cannot-call-method-hover-of-null

by KooiInc MeHere

HTML

<ul id="nav">
        <li><a href="#home">Home</a></li>
        <li><a href="#portfolio">Portfolio</a></li>
        <li><a href="#projects">Projects</a></li>
        <li><a href="#photography">Photography</a></li>
        <li><a href="#about">About</a></li>
        <li><a href="#end">Contact</a></li>
    </ul>

CSS

body {
    background: black;
    color:white;
    font-family: Arial, Verdana,  Helvetica, sans-serif;
}

ul#nav {
    width:100%; 
    height:50px;
    padding: 15px 0 0 0; 
    margin: 0;
    color: #c1c1c1; 
    position:fixed;
    font-size:16px;
}

ul#nav li {
    float:none; 
    height: 50px;
}

ul#nav li a {
    color:white;
    text-decoration:none;
    padding: 17px 5% 15px 5%;   
    -webkit-transition: all 1s linear;   
    opacity: 0.5    
}
    
ul#nav li a:hover {
    width:120px; 
    height: 100%;
    margin: 0;
    color: #ffffff;
    -webkit-transition: all 0.5s linear ;
    background: url(http://www.candlesandsupplies.net/Scarlet-Red-Color-Block-image.gif) no-repeat top left;
    opacity: 1    
}