Thank you all.
I've tried updating from the open app but the same result - "can't find server". This happens also if I try direct connection to Grisoft themselves OR ANY site which refers to the FREE version. However if I try to connect to the UK site which (misleadingly!!) calls itself AVGFREE (or something similar), no problem - except that it doesn't offer an update for the free version!
Eventually I found a site which offered a download of the latest version of the real free program - downloaded and tried to install - installation aborted because the version of Windows on my machine doesn't meet the program spec!!! ??? It has been meeting the program spec for about eight or nine years to date, so what's the difference now??
IF (and it's a BIG if) the win XP Prof SP2 isn't suitable for AVGfree, presumably it won't suit the paid for version either.
I hate the idea of leaving AVG, having had such reassuring function previously but it seems I have no option. Any suggestions for a suitable and equally accomplished replacement - free, if possible and, if paid for, most definitely NOT McAfee or Norton!!
TIA