         }
         else if(!columnGrouping && headerIndex != -1)
         {
-            selectedHeaderInfo = getHeaderInfo(columns[headerIndex]);
+            selectedHeaderInfo = getHeaderInfo(_columns[headerIndex]);
             selectColumnHeader(headerIndex);
         }
     }

        }
        return adgDescription;
    }
    
    /**
     *  @private
     * 
     */
    private function findHeaderRenderer(pt:Point):IListItemRenderer
    {
        var headerItem:IListItemRenderer;
        var xMatched:Boolean=false;

          {
              if (sortableColumns && 
                  selectedHeaderInfo.column.colNum != -1 && !isNaN(selectedHeaderInfo.column.colNum)
                  && _columns[selectedHeaderInfo.column.colNum].sortable)
              {
                  isKeyPressed = true;
                  selectColumnHeader(selectedHeaderInfo.column.colNum);
