BIND 9 Problem - DNS Forwarding

[Kh Linux]

Dear all:

I had been running both BIND 8 and Squid under SuSe 6.2 until recently when
I switched to RedHat 9 with BIND 9 and Squid from the 3 CDs.

Both in the old SuSe and new RedHat 9 now, I configure BIND to use
forwarding by adding to /etc/named.conf this:

         forwarders {
                N.N.N.N; // The IP of ISP DNS Server
        };
        forward only;


Now, BIND 9 always prints these errors below into /var/log/messages:

---
Oct 29 11:09:37 nslinux named[2787]: client 192.168.1.154#1264: updating
zone 'my.office.org/IN': update failed: 'RRset exists (value dependent)'
prerequisite not satisfied (NXRRSET)
Oct 29 11:09:37 nslinux named[2787]: client 192.168.1.154#1267: update
'my.office.org/IN' denied
---

And my 1 Mbps Internet connection (leased line) has always been saturated
since the switch-over. I don't know if that is the DNS forwarding problem or
a worm/spyware on my network.

Anyone has an idea? Hope for your kind and helpful response.

Regards,
Vidol