If you're referring to an erotic ghost story from 1990 that might have been made into a movie or is a part of a film, one notable example that comes to mind is "Ghost" (1990), starring Patrick Swayze and Demi Moore. While not strictly an erotic ghost story, it does involve a ghost and some romantic/erotic elements. However, it doesn't fit the bill if you're looking for something more overtly erotic.
If you're referring to an erotic ghost story from 1990 that might have been made into a movie or is a part of a film, one notable example that comes to mind is "Ghost" (1990), starring Patrick Swayze and Demi Moore. While not strictly an erotic ghost story, it does involve a ghost and some romantic/erotic elements. However, it doesn't fit the bill if you're looking for something more overtly erotic.