Using the "Active Directory Authentication" plugin (http://www.dokuwiki.org/auth:ad), a user group name can't include a ",". For instance, a user member of the group "Teachers, Professors & Assistants" can't login.
The code in adLDAP.nice_names($groups) function, in adLDAP.php makes a too basic assumption:
//more presumptions, they're all prefixed with CN=
//so we ditch the first three characters and the group
//name goes up to the first comma
I've been able to get a work around in my case replacing the line
But I'm not proficient enough with LDAP to know if this correction can be generalized.