Alot of poeple had probs with their free trials of office, either not running at all or only having x number of days left to run. This was because the ref no (or whatever) was out of date, when they were issued with a new no the probs ended. Sounds like something similar in your case. Badger the store.
Or, in my view better, dump nis altogether and use a free alternative such as avast/avg=antivirus and zonealarm=firewall +spywareblaster spybot, etc. Look on this forum for free av as.
PS you're quite correct 'but i will not need updates as any virus that come through can be deleted by the firewall.' is rubbish, just trying to get rid of you.
Hope this helps.