I am having the same issue. Purchased Avast Internet Security that included license for 3 machines, loaded on machine #1, no issue. This machine had Avast 4.? free version running on it. Installed v5 right over it and no issues at all. Machine #2 had Avast 5 free version on it. Again, installed the new IS5 program over it and everything works EXCEPT the firewall. The "Fix Now" button does not work nor does "Turn On". Both machines have XP-Pro with SP3. Machine #1 is wired to router, machine #2 is wireless. Windows firewall is still turned on for both machines. Tried the safe mode Avast un-installer found at the support website. No luck. Stuck for ideas. Put in a support ticket, but nothing back yet. Does anyone know if they are working on the issue? Thanks!