You may not know the server return status code illustration

Now, look at a more graphic illustration, hope to enhance memory (click on the image to see a larger image)

HTTP 400 - invalid request

HTTP 401.1 – Unauthorized: Login failed

HTTP 401.2 – Unauthorized: Server configuration issue caused login failure

HTTP 401.3 – ACL forbidden access to resources

HTTP 401.4 – Unauthorized: Authorization was Filter Denied

HTTP 401.5 - Unauthorized: ISAPI or CGI Authorization Failed

HTTP 403 - Forbidden Access

HTTP 403 - Access to Internet Service Manager (HTML) Localhost

HTTP 403.1 Disable access: Disable executable access

HTTP 403.2 - Disable access: Disable read access

HTTP 403.3 - Disable access: Write access disabled

HTTP 403.4 - Forbidden: Require SSL

HTTP 403.5 - Forbidden: Require SSL 128

HTTP 403.6 - Forbidden: IP address denied

HTTP 403.7 – Forbidden Access: Request Customer Certificate

HTTP 403.8 – Forbidden: Disable site access

HTTP 403.9 – Forbidden: Too many connected users

HTTP 403.10 – Forbidden: Invalid configuration

HTTP 403.11 – Forbidden Access: Password Change

HTTP 403.12 - Forbidden: Mapper Denied Access

HTTP 403.13 - Forbidden: Client Certificate Has Been Revoked

HTTP 403.15 - Forbidden: Client Too many access permissions

HTTP 403.16 – Forbidden access: Client certificate is not trusted or invalid

HTTP 403.17 – Forbidden: Client certificate has expired or is not yet valid

HTTP 404.1 – Unable to find Web site

HTTP 404 – Unable to find file

HTTP 405 – Resource is disabled

HTTP 406 – Unacceptable

HTTP 407 – Requirements Proxy Authentication

HTTP 410 – Never Available

HTTP 412 – Prerequisite Failure

HTTP 414 – Request – URI Too Long

HTTP 500 – Internal server error

HTTP 500.100 - Internal Server Error - ASP Error

HTTP 500-11 Server Shutdown

HTTP 500-12 Application Restart

HTTP 500-13 - Server is too busy

HTTP 500-14 - Invalid application

HTTP 500-15 - Request not allowed global.asa

Error 501 - Not implemented
HTTP 502 - Gateway error