Generally, a Not Found status error (usually a 404 HTTP status code) is returned when Googlebot attempts to visit a page that doesn't exist—either because you deleted or renamed it without redirecting the old URL to a new page, or because of a typo in a link.
And to learn how to remove 400 error page,check out the following link:
http://pcsupport.about.com/od/findby...ryNameOverride