add exception for MuseScore in AVAST anti-virus
Maybe no-one else is experiencing this problem, but on my PC I had to add an exception telling AVAST anti-virus that MuseScore 2.1RC from 27 April 2017 was safe to run.
There was no indication it was trying anything; it just would not start.
Once the exception was in place everything was fine.
This is the first time this has happened.