I have figured out my problem. For some reason I had to place brackets around the word Cast in my VB code. The Update statement now looks like:
UPDATE MovieDetails SET Director = 'Tim Burton', ReleaseDate = '23 June 1989 (USA)', Genre = 'Action', [Cast] = 'Michael Keaton, Jack Nicholson, Kim Basinger, Robert Wuhl, Pat Hingle, Billy Dee Williams, Michael Gough, Jack Palance', Length = '126 min', Rated = 'PG-13' WHERE (DetailsID = '6cd0bf88-bcef-4c50-a083-6c8261c94149')