We need to know more about what is the user doing
If you try to access manually /adfs/ls/
(by doing a GET without any query strings, without being redirected in a POST) it is normal to get the message you are getting. There's nothing there in that case. But if you are getting redirected there by an application, then we might have an application config issue.
Maybe you can share more details about your scenario? Or a fiddler trace?