Complex sentence: Goldenberg had previously written a few script pages for the first Harry Potter film "Harry Potter and the Philosopher's Stone" (2001) and while the producers liked them, they ultimately picked Steve Kloves to do the screenplay.
Split into simpler sentences: Goldenberg had previously written a few script pages for the first instalment in the "Harry Potter" film franchise, "Harry Potter and the Philosopher's Stone" (2001). While the producers liked them, they ultimately picked Steve Kloves to do the screenplay.