I assume you are refering to the error codes that a when server produces when it can't serve the requested page. An error 404 for example is a page cannot be found error. It's possible the link has changed or the content your looking for has been deleted. This is fairly common on the net. I call them dead links. Some search engines like Google (
http://www.google.com/) can serve up an cached copy of the page by clicking on the word "cached" below the returned search. I frequently use this feature when looking at old information.
Here is a list of the error codes (
http://www.the-eggman.com/seminars/html_error_codes.htm)
Code Description Comment/Reason
100 Continue
101 Switching Protocols
200 OK Action complete successfully
201 Created Success following a POST command
202 Accepted The request has been accepted for processing, but the processing has not yet been completed.
203 Partial Information Response to a GET command, indicates that the returned information is from a private web.
204 No Content Server has received the request but there is nothing to send back. (Empty Document)
205 Reset Content
206 Partial Content The requested file was partially sent. Usually caused by stopping or refreshing a web page before it loads.
300 Multiple Choices The request could fit multiple files.
301 Moved Permanently Requested a directory instead of a file. The web server substituted the index.html file.
302 Moved Temporarily
303 See Other
304 Not Modified The cached version of the requested file is the same as the file to be sent.
305 Use Proxy
400 Bad Request The request had bad syntax or could not be interpreted.
401 Unauthorized User failed to provide a valid user name / password required for access to file / directory.
402 Payment Required
403 Forbidden Access to a protected or private password protected folder was attempted.
404 Not Found The requested file was not found.
405 Method Not Allowed
406 Not Acceptable
407 Proxy Authentication Required
408 Request Time-Out The server did not respond in the allocated time.
409 Conflict
410 Gone
411 Length Required
412 Precondition Failed
413 Request Entity Too Large
414 Request-URL Too Large The submitted URL was too long to be interpreted by the server.
415 Unsupported Media Type
500 Server Error The server encountered an unexpected condition which prevented it from fulfilling the request
501 Not Implemented The server does not support the service required.
502 Bad Gateway
503 Out of Resources The server cannot process the request due to a system overload. This is usually a temporary condition.
504 Gateway Time-Out The service did not respond within the time frame that the gateway was set to wait.
505 HTTP Version not supported The Web Server does not understand the version of http used by the browser.