Hi David, Bob and thekochs,
This is just to let you know that I have accomplished the changes albeit in a slightly roundabout manner.
Firstly, although I had already set my system to show hidden files Bob, Windows Search did not find the avast5.ini file and somehow I missed it doing a visual search. It was there of course and eventually I found it. The next problem puzzled me - despite my user account Having administrator rights, after editing the file, Windows would not let save the changes. I got around this by making the Administrator account visible, logging on to that account and making the changes in that account. I have also modified the item in Avast 'Troubleshooting' to 'Load avast! services only after loading other system services' as you suggested David.
It now remains to see if the changes resolve the issue. Thanks for maintaining your interest regarding my trivial issue - I will report back when I have news. Cheers, Kes.