samba - Jun 2014 - dnsupdate: TKEY is unacceptable

I set up samba with BIND9_DLZ as described in the official howto. Bind 
seems to resolve all the provisioned names and the very basic samba 
connectivity seems to be established. According to the howto I tried:

samba_dnsupdate --verbose --all-names

and I get

dns_tkey_negotiategss: TKEY is unacceptable
Failed nsupdate: 1

for each entry. Any idea hot to troubleshoot this situation?

Thanks for your help,
  - lars.