https://www.howtoforge.com/community/threads/dns-ux-does-not-update-bind9-ubuntu.76786/ I put it over there in case someone else has problems, too.
A .err file is created when BIND rejected the config file. The reason are in most cases missing records, e.g. you might have missed to add A-Records for the NS-Records when the NS records are subdomains of the same zone. Take a look at the Linux syslog file, the reason for the error is listed there. And you can also get the error message on the shell by using the named-checkzone script from BIND.
