depending on the news server you are using, the post may have been "aged
out", ie deleted because it was "too old". Many news servers only keep
posts around for a couple of days. News as a whole is a really big beast,
and most ISPs are reluctant to manage it well; it is a full-time job for
at least one person, perhaps more. [FWIW, my server has over 37,000
groups, w/ messages going back 5 years! It is HUGE, and not very fast. My
reader is configured to never read more than 1000 headers back, or I'd
never be able to enter a group like this one w/o going and making a pot of
coffee.]
try google GROUPS, they keep stuff around for a long long time. Be sure to
seach in GROUPS, not web.