The actual biding im using is:
sudo /usr/local/ns/bin/nsd -t /usr/local/ns/config-fd6prod.tcl -u nsadmin -g nsadmin -b 104.251.214.8:80,104.251.214.8:443.
Are you aware of the fact, that the error message you have provided above reports a different IP address, namely 104.237.4.53:80?
Still wondering whether your server provider might have changed the IP address of this host...