Can't see TrueTime server

I have a TrueTime NTP server that I’d like to hook up to, using ntpd under
QNX 6.3 SP 2. Even though my QNX machine and the server are both plugged
into the same hub, on the same net, the QNX machine cannot see the server.
ARP apparently is not picking up the MAC address of the server.

The QNX machine can see Windows machines on the same network, and those
Windows machines can see both QNX and the server just fine, which leaves me
very puzzled. I even tried manually entering the MAC address of the server
into the ARP table on the QNX machine, to no avail.

Any advice or comments as to why this is happening would be appreciated.