This tutorial will show you a few of the most common error codes a server may return. There are many different error codes that a server can deliver,some even for the same error. These are probably the most common ones that a visitor might see, and ones that you might like to build custom error pages for, just to continue the flow of your website.
401 - Unauthorized
Access to this page requires user authentication, which either has not yet been provided or has been provided and failed.
403 - Forbidden
The request was a legal request, but the server is refusing to respond. Unlike a 401 Unauthorized request, authenticating will make no difference, and the request should not be repeated.
404 - Not found
This response code indicates that the visitor was able to communicate with the server, but either the server could not find what was requested, or it was configured not to fulfill the request and not reveal the reason. Error 404 should not be confused with "server not found" or similar errors, in which a connection to the destination server cannot be made at all. This status code is commonly used when the server does not wish to reveal exactly why the request has been refused, or when no other response is applicable.
500 - Internal Server Error
This code indicates that the web server has encountered an unexpected condition that prevented it from fulfilling the request. Basically, something has gone wrong, but the server can only supply the visitor with an unspecific reason for the failure.