The meanings of these error codes from the web server are:
401 Authorization RequiredThis error message indicates that a website visitor tried to access a password-protected page without authenticating (with a valid username and password).
403 ForbiddenThis error code means that access to the page the visitor is requesting is not allowed. This can be due to a special rule in the configuration of the web server, or due to the specific file system permissions of the file. An example rule in an .htaccess file that would cause this message is this:
deny from 1.2.3.4
where 1.2.3.4 is the IP address of the visitor.This error can also be caused by the file lacking read permissions. In that case, the web server will not be able to read the file, and this error message would be displayed.
404 Not FoundThis simply means that the requested file is not there.
412 Precondition FailedThe error means that the request triggered a mod_security protection on our end. You can learn more on this matter in the Error "412 Precondition Failed" (mod_security2) article.
500 Internal Server ErrorThis can be the most confusing error message, because it can be caused by many things ranging from server and permission problems to application errors and script misconfiguration. More sample causes for the error can be found in our Error 500 (Internal Server Error) article. Information about the actual error message is recorded in the server's error log, which you can review via the Logs section in the Control Panel.