YoGen Vocal Remover tries to remove lead vocals from stereo sounds. Quality of vocal removal depends on how songs are recorded and mixed. This software works very well for vocal tracks that are "up in the middle" of the stereo mix. Other placement of the vocal in the stereo field can not be removed. If songs are not recorded in this way, their vocals are not removed at all. This is why some songs work great while others do not.
Therefore you do not expect this software to remove vocals 100% nicely. In many cases, however, it will be useful enough to remove lead vocals.