I assumed that you were making your own game when you encountered this problem.
But now it sounds like you were playing someone else's game...?
Well either way, loading the mp3 file into Audacity would reveal whether it really is an mp3 file and not something else, like an ogg file renamed to mp3.
Also, if it is an mp3, but there's something wrong with it, like it's corrupted, then Audacity will reveal that too.
Finally, Audacity might be able to save it to an mp3 file that is usable, and if it can't then you save it as a wav and put the wav in the Music folder.
And doing any of this will not affect your ability to play other games with mp3's. (I don't know where you even got that idea)