It seems the file /etc/nagios-plugins/config/nt.cfg has an extra -v in the arguments.

Code:
define command {
 command_name    check_nt
 command_line    /usr/lib/nagios/plugins/check_nt -H $HOSTADDRESS$ -p 12489 -v $ARG1$ -v $ARG2$
}
This causes check_nt to throw an error and outputs the expected syntax. Removing the -v before $ARG2$ seems to have fixed it.

Has anyone else had this problem?