Domain already hosted by your DNS server

Hello, i am using webmin/virtualmin for few years and never had any problem…

Now i have very strange problem - my domain example.com is created as virtualmin server and in DNS there is zone example.com but when i check enabled features i can get to be “checked” DNS server.

I get this message Failed to modify server : The DNS domain example.com is already hosted by your DNS server

Can you help me with this ?

I came across something similar. I think I solved it by restarting the named service. The domain name was cached in memory.

service named restart