Why is on status span no search results?

i have written some jQuery code for my wordpress plugin :

  jQuery("#kd_nr_search").autocomplete({
  minLength: 2,
  source: function (term, response) {
          jQuery.post({
              url:ttstickerz_object.ajax_url,
              data: {
               search: term,
               action: 'search_kunden_nr'
              },
              method: "POST",
              dataType: 'json',
              success: function (data) {
                response( jQuery.map( data.kunden, function( item ) {
                  jQuery.each(item,function(i,val) {
                     val.label = item.name;
                  });
                  return item;
                }));
              },
              select: function(event, ui) {
                alert(ui.name);
                return false;
              }
          });
          }
      }).data("ui-autocomplete")._renderItem = function( ul, item ) {
  return jQuery( "li" )
    .append( "a" + item.name + "br/a" )
    .appendTo( ul );
};

but nothing is happen, no list is showing, nothing.

if i write a alert command in the success part like this :

              success: function (data) {
                alert(data);
                response( jQuery.map( data.kunden, function( item ) {
                  jQuery.each(item,function(i,val) {
                     val.label = item.name;
                  });
                  return item;
                }));
              }

it shows the correct response from the ajax query...

but nothing is listed.

any ideas ?