blockUI - Object does not support this property or method

blockUI - Object does not support this property or method

I am using jQuery in my jsp for AJAX hits. However, when I use blockUI the page displays an object not supported exception.

My jsp has the following and the jQueries work fine.
  1. <head>
  2. <script type="text/javascript" src="<c:url value="/scripts/jquery-1.4.min.js" />"></script>
  3. <script type="text/javascript" src="<c:url value="/scripts/json.min.js" /> "></script>
  4. <script type="text/javascript" src="<c:url value="/scripts/jquery.blockUI.js" /> "></script>
  5. <script language="javascript" type="text/javascript">  
  6.     $(document).ready(function() {
  7.         $("#dropDown").change(function() {
  8.             alert("NEW");
  9.             $.blockUI({ overlayCSS: { backgroundColor: '#00f' } });
  10.             setTimeout($.unblockUI, 2000);
  11.             selectRandom();
  12.         });
  13.     });
  14. </script>