Bob - in a default install of FSX, Addon Scenery is immediately above Propellor Objects. By 'above' I mean 'nearer the top of the screen'.
There are 115 default items altogether, and you should leave them as a group.
Did you try renaming your scenery.cfg (to scenery.cfg.old, for example) and letting FSX build a new one during a restart?
MikeW