Last time you updated TntMPD for Mac, you were asked to copy the new TntMPD into your Applications folder. Since there was an existing TntMPD in your Applications folder, your Mac gave you three options: "Keep Both", "Replace", and "Stop". You probably chose "Keep Both" so it added in your new TntMPD as "TntMPD 4" (since "TntMPD 3" and "TntMPD 2" also existed).
To get past this, just open your Applications folder (in Finder). If "TntMPD" exists, delete it. Then rename "TntMPD 4" to "TntMPD". I'd also recommend you delete "TntMPD 2" and "TntMPD 3" as well.