Many of the posts you find by search will return this reply. Looks like the pages are still in the index, but probably no longer physically present. It's a known issue, and there's been discussion of finding a home for older posts and former versions of the forum.
Fixing it never seems to be a hot issue; my guess is that most of the affected info is outdated, so even if it were accessible, it may cause more confusion than help.
Still, something should be done either to put those pages up somewhere accessible or to delete the references. Thanks for mentioning it and keeping the issue from being forgotten.