HST51: Thank you for this post. I had the same exact problem on 17 Jan 2018. Download never stopped looking as though it was still downloading. I started downloading the "special definitions" last night, set my laptop to never go to sleep, went to bed. In the morning it was still showing the slidey green line icon for the download in progress!!!! Selected the boot time scan a 2nd time, waited about 3 minutes then closed Avast window, and reopened it. It was ready for the reboot time scan. Thanks to your post, really really helpful.