Some users reported that, for them to install AIS 7, they
1_ installed Avast Free 7;
2_ rebooted;
3_ added AIS license;
4_ rebooted;
5_ is necessary, Add/Remove Programs -> avast -> change -> add all components included in AIS;
6_ rebooted.
That was with clean installs. Step #5 (or similar) should be enough to update from AIS 6 to 7, but since the workaround worked for some...