Sorry to bring back an old thread, but I just had an issue with this error as well. If anyone still has issues with this, try editing the FSX.CFG file in AppData/Roaming/Microsoft/FSX and removing the default saved flight (the path after SITUATION=). This worked for me. Deleting a dozen assigned keypresses in FSX's control settings had not helped with this issue.
What preceded the error was when I saved a flight with a newly acquired Virtualcol Embraer 170. I landed there, saved after exiting into the taxiway, and then FSX ran out of RAM and crashed when PF3 was still running. I re-ran FSX and accidentally quit PF3 normally when I wanted it to be forced quit. I parked the aircraft at the gate and saved it as a new default flight. PF3 first showed me that error either after I tried to re-run it after re-running FSX OR when I used it with my next flight - I can't remember.