WebService "Service Unavailable" Error

If you get "Service Unavailable" error message when you trying to run webapplication, check the follows issues:

• The application pool is not running.
• The application pool account uses an incorrect password.
• The application pool account is not a member of both the IIS_WPG group and the STS_WPG group on the server.

Thanks to liron for it post : http://lirliron.blogspot.com/2009/03/webservice-service-unavailable-error.htm