Hi all and @MartinZ
I solved my problem with the key provided in the post that DavidR pointed in his answer
W11332244H9900A0420-8MRTR8W5
It's worked for avast 11.2.2262 published the 27/04/2016 running on XP SP2.
Avast free for 1 year.
Have a nice day.
Martin
Good to hear.
Reference your other points:
I, as an avast user can't speak for avast. But many years ago if I remember rightly if the program wasn't re-registered it could well have been unprotected.
The major problem as I (an avast user) see it is old programs aren't retrospectively updated, that is only for the current version. If avast changes something such as this re-registering, the program may not be able to cope/cater for the changes.
Hopefully this workaround by Avast will last for some time to come.