It sounds like you're sending a request to the server that doesn't specify a specific file, i.e. http://www.mydomain.com rather than a specific file such as http://www.mydomain.com/somefile.html. When you do that the server looks for a file with the default name in the directory to send to the user; if it doesn't find one, it will list the contents of the directory unless the server software is configured not to. In that case, since it isn't permitted to show the contents of the directory (it's a potential security problem), it instead displays an error message, Directory Listing Denied.