The issue in this specific case was scripts/driver only caught ImportError on a try: of importing mm_cfg and the exception here is SyntaxError. I have changed it to catch any exception and also indicate the traceback could be in the web server logs.
** Changed in: mailman Importance: Undecided => Low
** Changed in: mailman Status: New => Fix Committed
** Changed in: mailman Milestone: None => 2.1.27
** Changed in: mailman Assignee: (unassigned) => Mark Sapiro (msapiro)