Check you have configured the firewall in Avast to allow file sharing traffic, it’s done under system settings, I believe it’s called.

If that doesn’t help, notice that the firewall in Avast 2014 is buggy as hell, lots of other people have the same problems. Try to remove it completely and see if it works. Then install Avast again, and see if it still works. If it stops working, check you have configured the firewall in Avast to allow file sharing traffic, it’s done under system settings.

Good luck, you are going to need it with Avast 2014.