Disappearing scenery

Hi all I have a question about airport fs2002 pro i am at the moment trying to put a small island ofthe coast of Irelandwhen i go over the existing defult island i get ot a certain point and then the whole scenery that i have createddisappears like the bermuda triangle it seams to be once i go over 94 points the whole lot goes.also on certain points of the island i am putting some small hills but when i pull the points into the same area the hills also disappears i ahve tried putting other textured polygons and they don't show at all , is this a land mesh issue or am i just going insanei have flatened the areaPlease sombody help meAll the best