This message will appear if the domain is already on the system. Â The way that DirectAdmin checks to see if the domain is already on the system is by looking in the named.conf file. Â (RedHat: /etc/named.conf, FreeBSD: /etc/namedb/named.conf)
If you are positive that domain has not been added anywhere in DirectAdmin (use "Show All Accounts" in the Admin Panel), then it should be safe to remove the zone from the named.conf file either manually, or by removing the zone from Admin Panel -> DNS Admin. Â Then you should be able to add the domain.
Be sure to backup the zone if you do not wish to lose the dns data.
With the addition of the Multi Server option, dns can now be hosted on other DA servers. Â Ensure that any Servers you have listed in your "Admin Level -> Multi Server Setup" page also do not have the domain in their named.conf files. Â If you disable the "check domain" option, then that server will not be queried.