I've got a similar problem. I have the secondary server mentioned in the Primary's "name server" tab. When I add the zone to the secondary server, it immediately says "Zone not loaded by DNS server". I can ping all the appropriate IP addresses (from both primary and secondary), so everything can see everything else.. The secondary server does have two NICs and 2 IPs on each..
I've tried deleting the zone, re-adding it, restarting DNS service..
If I change the primary's server's zone transfers to "Any server", it works..
Is leaving it to "Any Server" a security risk? The servers are co-located and internet facing (behind a firewall), but need to be accessible via the Internet for DNS requests - DNS ports open through the firewall to currently allow this.