You might get such an error message for several reasons, including:

• The site you're visiting might be busy or temporarily down. This can happen a lot, especially with overloaded (or extremely popular) sites. Try again later; such overload problems are usually fixed with time.
• The site might be denying people access, intentionally or unintentionally. You might consider trying to contact the web master directly via email.
• The site simply might no longer exist. If you follow a link to a site that no longer exists, the information in the search database is corrected by our normal content refresh processes.