Your DNS cache stores the locations (IP addresses) of pages you have recently viewed. If the location of the page changes before the entry in your DNS cache is updated, you will be unable to access the page.
If you are encountering a high number of HTML 404 error codes, you may need to flush your DNS cache. Once you clear your DNS cache, your computer will query nameservers for the new DNS information you require.
For more information about the HTML 404 error code, please visit the HTML 404 wikipedia article.
The methods detailed below allow you to remove old and inaccurate DNS information that may result in 404 errors.