A number of people have reported failed authentications with ntlm_auth when using Samba and Active Directory. This issue appears to have been tracked down, and a patch posted:
https://bugzilla.samba.org/show_bug.cgi?id=6563 A few people have reported that the patch works, but the Samba team is looking for more widespread testing. We're asking that anyone who has the problem try the patch, and post a response on the above bug report reporting success / failure. Thanks to everyone for the reports, and the patience while this was tracked down. Alan DeKok. - List info/subscribe/unsubscribe? See http://www.freeradius.org/list/users.html

