PostprocessBuildPlayer wont start on Unity 5.1.1f1, Mac

The PostprocessBuildPlayer script is written in Python, it is executable and located in the folder Assets/Editor, and yet it wont start. What else could have gone wrong with it?

The script is from the Hockeyapp plugin (from their git, not from the asset store) and everything else was implemented as instructed on the git readme.

What happened is that the script encountered a problem and did not finish with execution. Unity does NOT notify clearly when that happens! I checked the Editor Log (on the Console view) and there it was, the crash output.

In any case, the PostProcessBuildPlayer works, but crash/error reporting in it is a bit obscured.