The Sun Sentinel has an article about the Encyclopedia Brown series and the multiple attempts to "franchise" the books over the years. It is an interesting look at how rights to books can be divided. Supposedly, Ridley Scott is interested now. The author of the books, Donald J. Sobol is not keen. He currently does not hold the movie rights.
The list of those who have taken an interest in Encyclopedia Brown over the years, only to have the project come to nothing, is a jaunt through Hollywood over the past three decades.
Among others, Warner Bros. was on track to make the film in the 1980s, with Chevy Chase and Goldie Hawn in the starring roles. That fell apart over legal complications, including the Sobol lawsuit.
Aaron Spelling saw it as a television show in the 1980s, and Johnny Carson at one point wanted it for his production company. Hanna Barbera, the animation company, envisioned the detective stories as a hand-drawn animated series. Anthony Hopkins offered to direct and act in the project as a film after meeting Deutsch in Utah in 1989. And an executive producer of Waterworld, Andrew Licht, wanted to take it on in 1995.