[edit: if your movie file is a mp4 or m4v, it might have internal metadata which point to the other movie. You wanna make sure it contains either the correct ‘title’ tag or none at all]
Try first the Plex Dance with the movie.
If this doesn’t help, make sure to have a subfolder for this movie
Like so:
Movies
How the Grinch Stole Christmas! (1966)
How the Grinch Stole Christmas! (1966).mkv
then put a text file besides the movie file which contains the IMDB ID for this movie (or maybe the complete URL http://www.imdb.com/title/tt0060345/).
then rename the text file to How the Grinch Stole Christmas! (1966).nfo (yes, change the filename extension from .txt to .nfo)
Plexdance the subfolder of this movie again.