Denied Update

[Justin Thomas]

I am receiving this message in me message log:

Sep 16 20:46:05 unix named[133]: denied update from
[my.ip.address.here].1313 for mydomain.com

I edited out my real ip address and domain name, of course and the 1313
increases each time the message appears in the log.  The message shows
up at random intervals, sometimes within 2 hours and sometimes within 5
minutes.  I have set my firewall to allow all traffic through.

I have not noticed an actual problem yet, but rather want to be
proactive about solving it.  What does this message mean?

Thanks for any help,
Justin