JQuery :: Document Ready Not Executing When Page Loads

I have an html page with a lot of JavaScript functions that all work fine. Then I decided to add a jQuery function, but the document ready is not executing when the page loads. As you can see below I've added the document.ready function at the top of the page, below the links. And below that are the JavaScript functions that were there all along. Why the document ready function doesn't execute? (I don't see the "ready" alert, and the jQuery isn't working.)

<link rel="stylesheet" type="text/css" href="css/real.css" />
<script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript">
$(document).ready(function(){
alert("ready");
$(".CheckBoxClass").change(function(){
if($(this).is(":checked")){
alert("adding LabelSelected class");
$(this).next("label").addClass("LabelSelected");
}else{
$(this).next("label").removeClass("LabelSelected");
}});
});
</script>
<script type="text/javascript" language="javascript">
function showImage(image) {
image.style.visibility="visible";
} function hideImage(image) {
image.style.visibility="hidden";
}