GOES BACK TO SCENERY LOAD THEN CTD

After reloading all my FSX stuff on to another computer, I'm getting an odd CTD problem. FSX loads as normal, then after a few minutes of everything looking good at the airport it goes back to the black screen and the info box saying "loading air sea and land vehicles". Sometimes it then goes back to the airport and it's fine, sometimes it crashes and I get a "fatal error" box. It seems to be the same for all add-ons or no add-ons. On one or two occasions the it's happened at the destination airport, at the end of the runway I've just landed on - the black screen and the loading box, then it picks up as though nothings happened!Any ideas???Roy