I'm getting no definition updates since updating to the latest version of Avast. I'm running 13.1, virus definitions 17111704, with Firefox Quantum (57) and macOS Sierra 10.12.5. All I get when clicking on "Update" is "An error occurred during updating", and it means it! Of course I'm used to getting a variety of such erroneous messages such as this but in the past it has successfully updated and given me a confirmatory dialog box to that effect, but now it's not erroneous! Am I alone? I've tried switching off any potential interferences that I can identify (inc Hands Off! or Malwarebytes) which might be over-enthusiastic in protecting me, but no change. Is anyone else having this updating problem? I'd be grateful. Thankyou.