             // implementation.
             oldStepSize = stepSize;
             stepSize = Math.abs(viewport.getVerticalScrollPositionDelta(
-                (increase) ? ScrollUnit.DOWN : ScrollUnit.UP));
+                (increase) ? NavigationUnit.DOWN : NavigationUnit.UP));
         }
         super.step(increase);
         if (viewport)

        if (viewport)
        {
            var vpPageSize:Number = Math.abs(viewport.getVerticalScrollPositionDelta(
                (newValue > value) ? ScrollUnit.PAGE_DOWN : ScrollUnit.PAGE_UP));
            super.animatePaging(newValue, vpPageSize);
            return;
        }        

            // implementation.
            oldPageSize = pageSize;
            pageSize = Math.abs(viewport.getVerticalScrollPositionDelta(
                (increase) ? NavigationUnit.PAGE_DOWN : NavigationUnit.PAGE_UP));
        }
        super.page(increase);
        if (viewport)
