Something weird is going on here. Yesterday everything was working fine, but today the taxi and landing light switches on all aircraft (even default) do not work. They switch on momentarily then immediately switch off. What I mean by this is that the toggle switch (on the default Cessna for example) moves back to the 'off' position. I have even tried using the keyboard command and view from the outside. I see the landing light flash for a split second then it is off again.

It is especially strange as I have not modified anything in FS9. I did, however, install a Win7 update yesterday, although I cannot see how that would affect anything like this.

Has anyone come across this issue before?

I think I have solved the problem. It was Shockwave lights - I re-ran the SW utility and all now seems to work fine. Phew!