Thanks for that, folks, I finished up uninstalling and re-installing the free version of AVG on both machines and they both seem to work OK now. I presume that I must have unwittingly downloaded the free trial for the full version although I am equally sure that I very carefully selected the free version before.
Put it down to age.
I agree with LR about using the full versions on netbooks, my wife's Asus does to grind to a halt sometimes as AVG does its stuff. You can tell when its happening by the stream of invective coming from the sitting room at which point I feign deafness until it has subsided or when I fear for the physical wellbeing of the machine.
GG