erros on slave "server refresh: unexpected rcode (NXDOMAIN)"

[Gregory Machin]

Hi.
I have a bind 9 primary server and a bind 9 secondary server, I added
a new sub domain to the primary and as a slave zone on the secondary.
i have obviously missed something. What does :

named[13931]: zone domain.example.com/IN: refresh: unexpected rcode
(NXDOMAIN) from master 209.234.97.14#53 (source 0.0.0.0#0)
mean ??

As far as the primary server logs goes there is nothing that indicates
an issue .

Thanks