Error 400 – Bad request
This is a rare error, which occurs when a web browser makes a request that the
web server doesn’t understand.
Error 401 – Unauthorised
Some web pages require a user name and password for access. This error message
appears when they have not been supplied, or have been entered incorrectly.
Error 403 – Forbidden
The most common cause of this error is the lack of a default index page, or a
user trying to navigate a website’s folders directly. It can also occur if a
script is prevented from running by the web server.
Error 404 – Not found
This is the error that most people see, as it is given when a web address is
typed incorrectly or a particular web page no longer exists.
Error 500 – Internal server error
This is a non-specific error that can be caused by an error in a web script or
a problem with the server itself.