Owncloud + LDAP

People, I have an owncloud server with version 9.1, and I want to integrate them with LDAP server to manage users.

When i enable the application tool CAS user and group backend, i can´t to enable this application because I am receiving the following error

Text / html files are not supported

Did you read and follow the documentation?
https://doc.owncloud.org/server/9.1/admin_manual/configuration_user/user_auth_ldap.html
CAS User is different from "standard" LDAP ...