It's possible that:
* The title is incorrect: You might be thinking of a different title or year.
* The movie is less known: It could be a smaller production or a foreign film.
Could you please provide more information about the movie you are looking for? For example:
* Is it a German production? ("Neptun und Isolde" sounds like a German title)
* What is the genre? (Comedy, drama, fantasy?)
* Do you remember any plot details?
With more information, I can help you find the cast you are looking for!