dreamer

Hello, I've been trying to reduce/vocals from a stereo mp3 or wav file, but whenever I click on "Reduce Vocals" from the Special Effects sub menu, nothing happens, and when I play the file the vocals are just as strong as before. Am I doing something wrong, or does this mean that the file isn't compatible with this effect? Shouldn't some sort of box pop up when this effect is selected, even if it is unable to reduce the vocals? Cheers, Tim