400 This is bad request error, First check you may be typing wrong URL name and server could not understand your request.
401 You are trying to open any unauthorized access site or page. Check your username and password if you are trying to open any webpage.
402 Payment Required Error
403 You are trying to open any forbidden page and you are blocked by that domain.
404 Here you are trying to open the webpage that was removed or re-named, also check the URL spelling.
408 This is time out error. you should send the request with in time that the server set for you.