Thanks for the advice - the freeze happens during a flight and happens on every flight, basically the instruments and scenery freeze but the sound carries on and the only fix is a CTRL ALT DEL back to the system manager. I have worked through the guide as advised but unfortunately haven't been able to isolate the issue, I also rebuilt the .cfg and flew without making any changes but again got the same issue. Interestingly if I keep trying the same mission then I seem to get further each time although this is probably just coincidence.