Enabling /disabling an NSMenuItem using MacOSLib

I am using a NSMenuItem (from MacOSLib) to create a status menu item. However, I cannot work out how to disable (gray out) the menu items. I tried the following code:

Dim MenuTest1 as New NSMenuItem
MenuTest1.Title = “Disabled Menu”
MenuTest1.Enabled = false

and then added this to the main NSStatusBar menu (using the sample code in MacOSLib). However the menu item is not disabled. Can anyone help?