I've got a weird intermittent issue across several servers with check_ntp.
I've changed my setup to use the (non-deprecated) check_ntp_time, but the error still crops up:
Date/Time: Thu Jul 10 05:50:36 PDT 2008
NTP CRITICAL: Offset unknown
The log on the server contains this right before the check fails:
Jul 10 05:51:40 prmx011 ntpd: synchronized to 10.101.16.115, stratum 3
command_line $USER1$/check_ntp_time -H $HOSTADDRESS$ -w $ARG1$ -c $ARG2$