This property is not supported in the .NET 4.0 rendering mode. If this property is required, you can set the menu to the .NET 3.5 rendering mode by adding the following in the page's code:

menuInstance.RenderingCompatibility = new Version(3, 5);

When a dynamic menu item contains additional items at the bottom of the menu, an image is displayed to indicate that the user can scroll down to view additional menu items. Use the Menu.ScrollDownText property to specify the alternate text for this image. The text that you specify provides assistive technology devices with a description of the image that can be used to make the control more accessible.

The value of this property, when set, can be saved automatically to a resource file by using a designer tool. For more information, see System.ComponentModel.LocalizableAttribute and ASP.NET Globalization and Localization.