Since downloading the DSBDesign Tornado for FS2004 (which is excellent by the way if you've not got it!!), I get errors.
Firstly when FS2004 is starting up I get the error "Flight Simulator has detected potentially incompatible aircraft or software. File: FSSound.dll". I'm then asked if I want to load or disable - and I usually click "No".
Also when loading the Tornado up I get two errors about "\guages\XMLSound.GAU".
It's worth noting that I have re-installed FS2004 and then the Tornado aircraft and I STILL get this error.
Final question (I promise! ) should I have "contrails.cab" in my \guages folder???
I would remove both FSSound.dll and XMLSound.GAU to a temporary folder then run FS9. You won't get the error msg. anymore and it should not affect the flight sim.