Comment 15 for bug 74279

It looks like this is not a F-spot error, but a libgphoto2 one. I tried installing gthumb and it can't read the D300s camera either. It reports "An error occurred in the io-library ('Unspecified error'): No error description available".
What is also interesting is that the trick of having both CF and SD cards installed in the D300s is not a real fix - it allows you to load F-spot when it auto-detects the camera (though you get an error message), but if you don't launch F-spot initially, you can't access the camera by gthumb or by trying F-spot later.