I have previously asked about mysterious failures of ntpd to start on some
systems, which I thought might be ipv6-related.

It's more general; systems with a lot of interface aliases need a higher open
files limit for ntpd, which cannot be configured to attach to only-some
addresses, but rather, attaches to every alias separately.

The solution, in my case, was to add "ulimit -n 256" to /etc/rc.d/ntpd.

-s