This article covers method to resolve the error, Virtualmin System is not setup to use itself as a DNS server. In fact, this error happens as a result of changes in your IP address being obtained by DHCP. By default, the DHCP client will set a number of things, including the DNS servers.
Virtualmin is configured to setup DNS zones, but this system is not setup to use itself as a DNS server. Either add 127.0.0.1 to the list of DNS servers, or turn off the BIND feature on the module config page.