La Demoiselle et son revenant (1952)

Rosette is young and charming but she is crippled so she cannot make the most of her life. Which upsets Jules Petitpas, a single inventor, her eccentric but kind-hearted neighbor. Jules pledges to help her by creating a potion that will cure her. Unfortunately he dies before being able to achieve his aim. But a promise is a promise, and the good man comes back to the land of the living as an ... ectoplasm! And he manages to involve a whole tribe of ghosts to assist him in the noble task of saving the young lady. All is well that ends well.