Done it - I hope
The problem was that I'd been trying to use the folder Alwil software
listed in c\:program files as suggested in the other thread but it turns out that it isn't the right folder anymore. Avast V.6 is in new folder labelled Avast
which I hadn't noticed. Quite why the Alwil folder is still listed in c\:program files despite being redundant I don't know.