fs crashes after scenery is added

Hianyone able to tell me why the following is happening?I have altered the default scenery for RAF waddington.Everything works ok untill i place three aircraft macros at a sertain location.After that, when i try to start flightsim it updates the scenery files ok but when i try and goto the airport just altered it gets so far through the loading process then just stops.In this certain location there are a couple of excludes. The scenery works just fine if i place the macros somewhere else so it cant be the macros. The exludes dont seem to bother any other macros at this location either, IE buildings and so on. aalso, if i place just one or two aircraft macros at this location i can actually get fs to load but when i take off the thing crashes as just described.I'm compleatly baffled..any help would be appriciated.