Does the subject want to ask "what is the reason for the failure of theoretical training call server 4 10"? The URL of the original web page is invalid. The 40 1 page is a common mistake in accessing the theoretical training website and using the server. The most common error prompt is 40 1NOTFOUND. The 40 1 page is the page returned when the user inputs the wrong link. Calling the server means that the web page pointed by the link does not exist, that is, the URL of the original web page is invalid. This problem can be solved by checking whether the URL is correct.