The error is due to your syntax in the second call statement. There is not an assignment operator in the 'with' clause. Instead, you use the 'as' clause to set a value to a variable.
I didn't know try to fix your query, as it is really a convoluted approach. You can use the following query if you are just interested in the list of unique genres.
match(n:Movie)-[:IN_GENRE]->(g) with g.name as genre, count(n) as noOfMovies where noOfMovies = 1 return genre