Can you explain what you mean by "writing a letter on Netscape"?
All I can think of at the moment is that you are subscribed to and using Newsgroups, but one of the subscriptions has expired. Not a subscription in the normal sense, ie you don't have to pay to subscribe, but you have to re-subscribe to the newsgroup in question.
If that is what is happening, then refresh your list of newsgroups, find the one that has expired, and if you want to continue downloading it, select it and re-subscribe.
I keep getting an expired news group certificate popping up whenever i am writing a letter on Netscape. I have no idea how to get rid of it. Any suggestions please. I have an XP and am not very bright as far as computing goes. Thanks Edith.