Well that seems to have sorted that OK , once I updated VPS manually to 111206-2.
What I don't understand it that on the first indication today after PC started, Avast recommended Delete followed by boot scan. The latter was clean and PC continued to start with no further warnings. I turned pc off again about an hour later, and later still I started up to the same warning, with the same recommendation. It appeared not to have deleted the file. It was at that point I consulted this thread whilst I still had the warning up, and took the advice to 'Ignore'.