Well, as always with these things, I can only say what worked for me.

I ended up (after quite a bit of pain) finding the Norton firewall program list and noticed that I had conflicting entries for MSN Messenger. One was Permit all and one was Block all. Not quite sure how they got in there – I have not configred any special rules so I can only assume a) I was drunk one night b) my lodger did something accidentally or c) I had some malicious code which amended the settings.

of these, a) is by FAR the most likely!

I got rid of all entries in Norton and then re-ran the application and 6.2 sprang into life!

Then it configured its own access rules (for some reason I have three entries in there again, rather than one blanket ‘Permit’ but it seems to work so I shall meddle no more).