Cream Cheese tastes sour

As a first attempt at making cheese, I decided to try and make cream cheese from 1 gallon of whole, vitamin D milk, a mesophilic direct set Mad Millie starter (1/8 tsp), and 2 TBS diluted rennet.

Recipe: http://www.thefamilyhomestead.com/makecreamcheese.htm

I went with the maximum amount of time (18 hours rest and 8 hours hanging in hopes of a firmer, dryer cheese). However the result was a consistency similar to firm yogurt and distinct sour taste. All utensils, containers, etc were cleaned and sterilized (boiling water) before use and a digital thermometer was used while heating the milk to 90 degrees before the initial culture was added.

Would someone be able to give me some tips on what I may have done wrong? Many thanks!

The sour note is probably coming from the really long rest (ripening) time. The same thing can happen if you use too much culture.

For a drier cheese, I would ripen a little less and hang a little longer.

These guys recommend scraping off cheese every few hours for a drier cheese as well.
http://cheeseforum.org/articles/wiki-cream-cheese-making-recipe/