What is this message mean?

[HeePok Lee]

Hi all!
I got these messages from /var/log/messages on DNS.
By the way, I don't know meaning of this messages.
Could you explain the meaning of this messages.
Thank you!!

messages : 1. Feb 24 18:16:17 ns1 named[18623]: Err/TO getting serial# for "acs.co.kr"
                    2. Feb 24 18:15:23 ns1 named[18623]: master zone "paka.co.kr" (IN) removed 


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