I bet that you had this case at least once. You upload a website to IIS and when somebody tryes to open the website they are asked for authentication when they shouldn’t. The reason for this is simple: you have a problem with the file/folder permissions. Check them and make sure that IIS has access to them.
This can occur on Apache as well. In this case, the users will see a massage ‘You don’t have permission to access / on this server.’ (They won’t be asked for a password). In this case, Apache doesn’t have access to the folder or you have selected an impossible to use for www-root folder. The best think to do is check the error log.