This is a common error for users implementing JQuery UI. Usually if you see this message, this could mean a few things:

– There is a syntax issue or bad link referencing the JQuery (min/full) JS. Use your debuggers to make sure the JS is loading.

– Similar to above this could also mean the JS cannot be loaded due to being contained in a folder which the site does not have permission to.

– If you are debugging locally and referencing the JQuery JS on an external site, make sure you have internet access and that the site which you are referencing to is up.

– The arrangement of script references may be in the wrong order. JS loads on runtime, so dependencies are important in placement of the script reference on the page. JQuery UI depends on JQuery(min), so (min) must be declared first or you will encounter the error.

As always, Firebug and other web development debuggers such as the one’s built into Chrome and IE are great tools to help you identify and resolve issues such as these.

Hope this may lighten someone’s day. 🙂

    <script src="../JQuery/js/jquery-1.4.4.min.js" type="text/javascript"></script>

    <link href="../JQuery/css/smoothness/jquery-ui-1.8.7.custom.css" rel="stylesheet"
        type="text/css" />

    <script src="../JQuery/js/jquery-ui-1.8.7.custom.min.js" type="text/javascript"></script>

References:
Firebug, http://getfirebug.com/
JQuery UI, http://jqueryui.com/