This issue may occur if the application pool for the virtual server is configured incorrectly in Microsoft Internet Information Services (IIS) 6.0. This issue may occur if one or more of the following conditions are true:

* 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.