These are probably the most common error codes that a visitor might see, you may like to create custom error pages for, error codes 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.
