PlasticSCM, Unity and El Capitan

I am trying to setup PlasticSCM (for the first time, ever) on Mac (El Capitan), and Unity (5.2.2f1) is complaining in the console when I switch the editor version control to PlasticSCM. The error is:

“PlasticSCM not installed.”

It is installed of course. Rather, I installed the package I found on the PlasticSCM download page. Am I missing a step somewhere in here?

I have the same problem with Unity 5.3.1 Pro