After checking on this problem at a flight simulator site, one of the visitors told me he had experienced an identical problem - he had left the airport and climbed to a certain altitude at a certain distance from his originating airport. When he reached this point he got the same error msg I did. This is an identical scenario to mine. This man said he had recently installed some add-on scenery in the same geographical area where the problem occurred; the add-on scenery had AFCADS (parking spaces for virtual and AI-controlled aircraft) plus AI aircraft flying assigned patterns within the scenery area. He went back to the scenery library in FS9 and disabled the scenery, then deleted it from the library plus deleted the files within the computer. Since doing so he has not experienced the problem. It appears what happens is a flight plan that crosses the add-on scenery's AI traffic plans, or is in the same area as the AFCADS within the scenery, competes with the sim for memory or other resources; it resents an outside object "muscling in" on its turf, and shuts down. I've deleted the scenery and AI aircraft, then went to a faster aircraft and flew through the same area at the same altitude (just so I could get to the CTD altitude faster) and nothing happened. Hopefully this has alleviated this problem.
What is the best registry cleaner available right now? Freeware if possible. I am running CCleaner, Microsoft Security Essentials, Malwarebytes, and WinPatrol on the machine, which has Windows XP Pro SP3 as its OS.