Question: What is a Soft 404 Error?
Answer: Normally when a working URL is requested the server returns a “200 OK” HTTP status code. Similarly, when a browser requests a URL that is not working (broken) the web server returns a “404 Not Found” HTTP status code. These HTTP status codes are read by browsers and crawlers but are not normally shown to visitors.
A “soft 404″ occurs when an broken link is requested but the server returns a “200 OK” error message anyway. Crawlers, like InSite, rely on the HTTP status code to determine if a link is working or not. Soft 404s are usually the result of a server-side misconfiguration. In some circumstances IIS can return incorrect status codes when custom error pages are used.
Usually sites using “soft 404″ errors will still have the text “File Not Found” (or something similar) on the webpage that is returned. You can configure InSite to look for this text and flag it as a broken link even though the HTTP status code is not a true 404 error. To configure this, look under the “Link Checker” tab in Advanced Project Settings.