The server may simply be busy. Try again later. The phone lines may be experiencing heavy traffic which slows down transmission. The server where the site is loaded may have limited capacity. There may have been an error in transmission.
Search engines can now find some addresses with less information.
The Internet is a continually evolving place. Sites move to different servers or are removed from servers. The search engines continually add new sites, but are slow to remove dead links. A few indexes place the best content match first. Check the search engine you are using.