Hi,
I have been a long user of Avast free, but decided to go to AIS. I paid the licence and updated to what seems a paid version of Free! The Firewall will not load and the GUI I have is the same as free but with Avast ISS at the top of the GUI. I have deleted, reinstalled but still the Firewall refuses to install, I have no other security on my system, so am at a loss what to do next? I have in essence a paid free version!
Cheers Bryan. 
Are you sure that you dont have an old third party firewall still installed on the system as that will stop the firewall being installed.
Here’s a fresh copy of AIS for you to try http://files.avast.com/iavs5x/setup_ais.exe.
Download and save the new avast copy then uninstall the copy of avast you have now from remove programs and reboot, have a look in c\programs and c\program data and delet the avast files and run a cleaner and registry scan with CCLeaner which will tidy up a few leftovers.
Now reinstall the new copy of avast you downloaded earlyer and reinsert the license file.