So I have the same problem solved in this post
AVG Community
Where my firewall prevents screen mirroring from working. It's fine when I turn the firewall off and fails when I turn it on, but I obviously want to keep it on when I'm screen casting.
So their solution was to allow file sharing in either the Enhanced Firewall settings page or in the Basic Rules section of the Firewall page. I'm not sure which, but I can't change either of them! It's not that the settings aren't being saved; I can't change them to begin with. It's very weird. Please help.