Boris Karloff was originally hired to play John F. Black, but it soon became clear that his severe arthritis would not permit him to undertake such a strenuous role. As such Karloff was switched to the part of Mr. Hinchley and Basil Rathbone was brought in to play Black.
The hearse coach used at the beginning of the film now resides outside of the Haunted Mansion at Disneyland.
In the early stages of development, the title at the time, Graveside Story, was considered as a parody of West Side Story (1961), which was popular at the time. That title and theme was discarded when it was felt that people wouldn't get the joke. The final title was chosen as a play on of William Shakespeare's Comedy of Errors.
Basil Rathbone apparently kept the cast and crew's spirits up by telling rude jokes and stories but never giving the final punchlines. Instead making the cast and crew think of their own endings.