hi, i am using jQuery BlockUI Plugin (v2) to block and unblock while loading and when on clicking some button.but my problem is masking is working fine while loading page but it is not working when we click button,here is my code

$("input[name^=filtera]").click(function(){
 $.blockUI({message:'<h3><img src="images/spinner.gif" /> Please Wait...</h3>'});
 $.ajax({
    url : "ChangeRequestSearch.action?last_date_modified=" + modifiedDate ,
    cache: false,
    success : function (data) {
      $("#tableLoader").html(data);
    }
 });
 $().ajaxStop($.unblockUI); 
});

i am getting the Error: $.blockUI is not a function

let me know what is the problem

Thanks Usman.sk