The given IP address does not react to ping or traceroute either. The route leading there looks like it’s a dedicated server as opposed to a home-hosted one?
So what Eric suggested is valid and should be checked. Additionally, this sentence here struck me:
Are you sure you mean NS records? You configured your Virtualmin to have those host names as NS records for “jmb-webserver.com”? Those entries then clash with what your registrar has recorded as NS for that domain:
jmb-webserver.com. 172800 IN NS ns.srv2.com.
jmb-webserver.com. 172800 IN NS ns2.srv2.com.
;; Received 111 bytes from 192.5.6.30#53(a.gtld-servers.net) in 130 ms
Those entries don’t hurt either though, since your Virtualmin is not hosting the jmb-webserver.com zone at all. It only would be if you configured the NS entries at your registrar too, which might or might not be what you want.