Same problem here, did a clean install of Windows 10 (last day of free upgrade), downloaded the latest Avast to the clean system and no protection, won't let me install license file, can't update the program or virus DB's... Tried multiple restarts, uninstalled several times using the uninstall utility.. tried installing different versions (free, internet security etc.) all result in me being told I'm not protected.. the built in resolve button does nothing...
I thought it was Windows 10 initially but after seeing the posts here am relieved that it's Avast, however VERY upset that such a release could be made public, I hope Avast think about extending the licenses of paying customers as a little compensation (as I've personally spent around 4 hours trying to fix the problem and I'm sure most people here have spent a good chunk of time on it themselves).