What is mean of this message?

[HeePok Lee]

Hi all!
When I use "ndc reload", I got this message from /var/log/messages.
And name server can not resolve this domain name.
But I can not understand what is mean.
Could you explain what is wrong?

Feb 15 10:03:39 ns1 named[239]: /etc/named.conf:35449: cannot redefine zone 'o-bro.com' class IN

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