BIND9 question/problem

[Armando Oliva Becerra]

Hello folks, do you have any idea about the following problem ??.
Customer has a name server started in his z/OS system, it is using the 
BIND4 (bind v4) without problems till now (some times it uses more CPU 
than expected), and he wants to migrate to BIND9 (in theory this should be 
an esay thing), but he has detected an issue and he doesn't know how to 
avoid it.  When the customer configures the name server to use BIND9, then 
the name server is started without problem, but no work is done, when a 
request arrives to the name server and it tries to solve it (sending it to 
a forwarder name server or do itself) no response is sent to the 
requester, all the conections are refused when the timeout is reached 
(every connection ends with a timeout error). The customer cannot see 
anything in the logs, and there si no error reported at startup.
Which info/traces whould be obtained for debugging ?.
Thanks in advance.
Armand