What I am trying to accomplish is using jQuery UI dialog method from my own JavaScript source code file. I have this kind of links in the Site.Master

<script src="/Scripts/jquery-1.4.2.js" type="text/javascript"></script>
<script src="/Scripts/jquery.validate.js" type="text/javascript"></script>
<script src="/Scripts/jquery-ui.js" type="text/javascript"></script>
<script src="/Scripts/Common.js" type="text/javascript"></script>  

Common.js is my own helper file. jQuery works fine there, but when I try to call for example:

$(document).ready(function() {
    $("#dialog").dialog();
});

I'll get "Microsoft JScript runtime error: Object doesn't support this property or method"

Any ideas why this happens? jQuery Works fine, but jQuery UI doesn't.