When using AFCAD it will let me add runways taxiways etc to DEFAULT airports but will NOT let me add them to an ADD-ON airport/scenery can anyone explain to me how to add taxiways etc to an ADD-ON airport/scenery the file Im currently trying to add to is bham_2k2.zip (EGBB)

If your addon scenery was built using pre-FS2004 scenery methods, it will supress the display of any FS9 airport AFCAD visual scenery, either the default data or any AFCAD file you try to add, regardless of priority level. AFCAD will still control the non-visual elements (these were part of the so-called AFD files in pre-FS9 scenery). There is also a bug, if the pre-FS9 scenery puts ILS systems with the same freq on both ends of a runway, only one will work in FS9.scott s..

Sounds good to me . . . but also check AFCAD2's File/Properties and see which AF2 file is actually being viewed (the path is at the bottom of that screen).