As odd as this may sound it was the Cessna 140. I don't know how or why, but the out of memory problem only showed itself if I was flying the 140. within a few minutes of loading the airplane I would get a default sound warning me that a shutdown was imminent. . .If I did nothing and continued to fly, I would get an error message that my computer was out of available memory and it would close the sim. However if I switched to any other airplane when that sound was ringing, the sound would stop and no message appeared and I could complete the flight unscathed. I tested a number of times and the results were always the same. I uninstalled the 140 cleared all reference to it, defraged, rebooted and reinstalled the 140. Thus far, no repeat of the OOM problem.
Just for the record, this was the first time, since I installed FSX/Accel many, many, many years ago that I had an OOM shutdown. Regardless of scenery, aircraft, other utilities added over time, or problems others had with OOM problems, I was never bothered by this until now.