KB #3770 - Captain Sim are saying that you should reinstall the 767 and see if that helps (make sure you have the latest version - 1.5).

KB #9035 - on the MS website for FSX, Windows 8 is not listed as a supporting OS for FSX, so the same applies to Captain Sim products. They may or may not work on Windows 8.

It seems to be a case of "pot luck" with FSX on Windows 8. I have had A LOT of problems with FSX on Windows 8, although it seems to have become more stable recently (because of updates?). I'm happy to stick with FSX on Windows 7 64bit.