Program crash on attempting to open file

MuseScore 0.9.6 -- Windows Vista SP2 64-bit

I created a small file and saved and re-opened it to work further without problem a number of times. Then came a time when I started the program and tried to open the file, to find that the program crashed at once. This happens every time I try again. Other files open without problem, and the backup file for the problem one seems OK. The two things I was doing in the session just before the problem were (a) inserting a few notes of a second voice in the upper stave of a piano layout, and (b) attempting without success to break the beam over four quavers to give two plus two.
I attach the faulty file and the backup.