
It should be located under C:\\documents and settings\yourusername\application data\microsoft\Combat Flight Simulator 3.0\uisel.xml
Or just delete the complete folder. You'll just lose your custom settings like last selected aircraft, custom keyboard settings, graphics tweaks etc.
Next search for and delete all files with extension bdp in your CFS3 installation root.
do the same with "zx" extensions.
All of the deleted files will be re-created when you next boot up CFS3.
Next run the CFS3 config tool from the start menu.
When done with all the above start CFS3, mind you, will take a while as it'll recreate all the deleted files.
Good luck!