Ok, that sounds to me as if it could be a problem of "order" of loading something. I have problems with the Simulator if I, for instance, load TiR before the lights program....if lights are started first, no problem.
I would try uninstalling the Spitfire and Accusim (Accusim first) from the "add remove programmes" item in control Panel, THEN go to the C:/Documents folder, find A2A/Spitfire and delete the spitfire directory (which contains the dat and log files).
Next reinstall the Spitfire "run as administrator" and then the Accusim pack likewise then the core update. Start FSX and see how you go, shut down windows and then go in again and see if the problem persists. Not deleting the dat and log files manually will more than likely preserve a "corrupt" file and no amount of reinstalls (without that step) will fix things (ask me how I know!!!
See how you go and let us know the result...if all else fails, another core update is in the works and the problem may vanish with that.