Goofs

After Horatio greets Nora in the barn, the two embrace, then fall into a haystack. Horatio tells Nora he sat on a pitchfork, she removes it, and holds it at arms length. The tines are turned away from Horatio. When she speaks her next line, the pitchfork is now in front of her, with the tines pointing toward Horatio.

At the start of the film, Nora reads a letter from George Washington in which he refers to the "United Colonies." Since the scene takes place in 1780, four years after the Declaration of Independence, Washington should have referred to the "United States."

The ghosts of Horatio and Melody cannot be seen by the living, but they each prominently cast shadows on the wall that would be seen.

In the prologue, set in 1780, Horatio Prim (Lou Costello) uses the term "teetotaler" to say he doesn't drink alcohol. The term (short for "total temperance") didn't exist until the late 19th century.

Melody's hair and clothing is 1940s style. Women did not wear trousers in 1780, and the zipper was not invented until 1893. Even if she is wearing men's trousers with a fastener other than a zipper, they certainly would not open on the side. Nor would she wear a bra.

When Horatio and Melody fall from their horses after being shot by the Revolutionary Army soldiers the ground is obviously a mat covered by burlap.

The spirits of Horatio and Melody are bound to Danbury Acres until doomsday or some evidence exonerates them of being traitors. It's never explained why Tom Danbury's memoirs, which confesses his own guilt but affirms that both Melody and Horatio were innocent of any wrongdoing, fails to constitute the evidence needed to set them free.

When Melody and Horatio are finally free to leave the estate at the end of the film, Melody hears the voice of her long dead fiance' and rushes off to join him in heaven, whereupon Horatio hears the voice of his long dead sweetheart Nora, and rushes to Heaven's Gate where she is waiting on the other side. However, she tells him he cannot enter just yet, because heaven is closed for Washington's Birthday! Shouldn't Melody also have been barred at Heaven's Gate for the same reason? Yet she wasn't there and clearly had already been reunited with her fiance'.

The officer curses Horatio and Melody's spirits to be bound to Danbury Acres until crack of doom unless some evidence proves them wrong. When Sheldon reads from Danbury's memoirs, Danbury states that Horatio had a letter of recommendation from George Washington. Danbury had seen and read the letter and had plans to use it to convict Horatio of treason in the event the British won the war. Since he has declared in writing the existence of the letter proving Horatio was a patriot, that statement alone should've been enough evidence to prove that Horatio and Melody (since she was working with Horatio at the time) were in fact not traitors; thereby lifting the curse upon discovery of Danbury's declared statement.

It's never explained how some random soldier has the power to control what happens to people when they die, based on his personal beliefs about what they did while living.