Most of media players nowadays give users tools for making their own playlists of either selected files or whole libraries. This is not a conversion actually, more of creating a settings from a list of audio files. Plenty of various playlist formats available, but not all may be supported in every media player.
But mp3 to pls conversion in proper file conversion sense is not possible, because playlists contain just list of songs and no audio data.
This conversion entry was verified by us and conversion was flagged as wrong or not possible.
Usually this happens when the conversion would try to convert different types of data between each other, such as audio to image, or it is not possible because incompatibility between programs, caused by closed file formats, very limited support etc.
If you find entry that you feel is flagged as bad wrongly, please tell us in the discussion below with as much as information as possible so we can fix it.