Hi,
maybe you did not remove all entries:
https://lists.samba.org/archive/samba/2014-August/183657.html
http://lists-archives.com/samba/95373-unable-to-join-dc-to-domain.html
Or maybe you run into a bug, that should have already been fixed:
https://forge.univention.org/bugzilla/show_bug.cgi?id=32893
https://forge.univention.org/bugzilla/show_bug.cgi?id=23360
Regards,
Stefan