We’ve detected that your 404 (file not found) error page returns a status of 200 (Success) in the header.
by Nick Musica, Internet MarketerIf Google Webmaster tools is giving you the error:
“We’ve detected that your 404 (file not found) error page returns a status of 200 (Success) in the header.”
You can confirm your server header with this tool from: www.seoconsultants.com
http://www.seoconsultants.com/tools/headers.asp