Osentalka's right. The deal Larry Niven has gives the full media rights to one of the studios. He is very supportive of the RPG, and supportive of an idea for a Known Space version, but the small print of his deal precludes it.
The manuscript Osentalka refers to is called 'The City in the Jungle' and was to be the first Ringworld campaign pack. It was the first project I was ever commissioned by Chaosium to write for and, had the book seen print, it would've been great. Ah, well.