Warning: Name server aren’t accesible

I installed a slave server in my DMZ. After a few issues to join it to my domain I got a problem with the name servers. I think, it’s correct to set the first name server as the IP address of the local server, the second name server to the domain master and the third one to the domain backup.
But I get this warning and name resolving doesn’t work. nslookup gives ;; Got SERVFAIL reply from 123.45.67.89, trying next server
What do I do wrong?

/var/log/daemon.log says

fp-dmz-ucs named[13021]: zone my.domain/IN: Transfer started.
Sep 26 20:23:25 fp-dmz-ucs named[13021]: transfer of 'my.domain/IN' from 127.0.0.1#7777: connected using 127.0.0.1#35685
Sep 26 20:23:25 fp-dmz-ucs named[13049]: client 127.0.0.1#35685 (my.domain): transfer of 'my.domain/IN': AXFR started (serial 10714)
Sep 26 20:23:25 fp-dmz-ucs named[13049]: client 127.0.0.1#35685 (my.domain): transfer of 'my.domain/IN': AXFR ended
Sep 26 20:23:25 fp-dmz-ucs named[13021]: transfer of 'my.domain/IN' from 127.0.0.1#7777: failed while receiving responses: CNAME and other data
Sep 26 20:23:25 fp-dmz-ucs named[13021]: transfer of 'my.domain/IN' from 127.0.0.1#7777: Transfer status: CNAME and other data
Sep 26 20:23:25 fp-dmz-ucs named[13021]: transfer of 'my.domain/IN' from 127.0.0.1#7777: Transfer completed: 0 messages, 304 records, 0 bytes, 0.010 secs (0 bytes/sec)