I was watching Bart & Guber's show two Sundays ago and Guber mentioned in passing, two or three directors, who couldn't sustain their careers, specifically mentioning Monte Hellman and Vernon Zimmerman.
I'm familiar with Hellman, but had never heard of Zimmerman and haven't been able to find out much about him. He isn't listed in any of the reference books I have and there isn't much there in the IMDB database. He wrote some screenplays in the 1970s and around 1980 made a horror flick called FADE TO BLACK that I haven't heard of.