I got the same error. If it's a small IP company the site owner may not be supporting all of its pages (this happens if they sell out or the owner dies, etc.)

Dropping the URL into Internet Archive's the Wayback Machine lets me take a look at it.

https://web.archive.org/web/20210121045932/http://www.robdempster.com/blogs/pmb/blog060.html

The main page shows up but the Wayback Machine never "crawled" the rest of the site (I didn't try every link, but none that I tried work.) But this might give you enough information to continue your search elsewhere.