Well this is getting to be a pain in the backside, it happened before and the fix was to stop and restart (didn't work), required a reinstall. Now its back again and no update for 15 days and manual update fails. Possibly since I reinstalled it after the last update failures.
No notification area warning about this, possibly due to the new problem reported below.
Not only that, but now I see that Avast Mobile Security (free) has stopped, this is the second time this has happened.
This is getting to a point to find an alternative that just works.