 
 package spark.components
 {
+import mx.core.mx_internal;
 import mx.events.PropertyChangeEvent;
 import mx.events.ResizeEvent;
 
 import spark.components.supportClasses.ScrollBar;
 import spark.core.IViewport;
 import spark.core.NavigationUnit;
+
+use namespace mx_internal;
 
 //--------------------------------------
 //  Other metadata

     *  @playerversion AIR 1.5
     *  @productversion Flex 4
     */
    override protected function viewportContentHeightChangeHandler(event:PropertyChangeEvent):void
    {
        if (viewport)
            maximum = viewport.contentHeight - viewport.height;

    }     

    /**
     *  @private
     *  Set this scrollbar's value to the viewport's current 
     *  verticalScrollPosition.
     * 
