Odd query issue

[Atkins, Brian (GD/VA-NSOC)]

I'm troubleshooting an issue with internal resolution of a domain. I
have 2 identical slave servers that resolve for domains that have been
delegated to our group. However, while one of the servers can
successfully provide the responses, the other cannot. I've checked with
the network gurus to verify there is not a possibility of a firewall or
IPS rule causing the issue, but came back empty-handed.

Here's the breakdown (please don't laugh at the antiques...):

Sun V210's running Solaris 5.8
BIND 9.5.1-P3

...
zone "blah.com" {
        type slave;
        file "/slave/db.blah.com";
        masters { 10.xxx.xxx.xxx; };
        allow-transfer { none; };
        allow-query { "all-clients"; };
};
...

# Query local server (one with issues) fails
$ dig www.blah.com.

; <<>> DiG 9.5.1-P3 <<>> www.blah.com.
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 1735
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
; www.blah.com.                   IN      A

;; Query time: 2 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Mon Aug  2 14:12:48 2010
;; MSG SIZE  rcvd: 29

# Query master directly or twin server from problem server succeeds
$ dig @10.xxx.xxx.xxx www.blah.com.

; <<>> DiG 9.5.1-P3 <<>> @10.xxx.xxx.xxx www.blah.com.
; (1 server found)
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 341
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
; www.blah.com.                   IN      A

;; ANSWER SECTION:
www.blah.com.            300     IN      A       10.xxx.xxx.xxx

;; Query time: 34 msec
;; SERVER: 10.xxx.xxx.xxx #53(10.xxx.xxx.xxx)
;; WHEN: Mon Aug  2 14:14:16 2010
;; MSG SIZE  rcvd: 45

Any ideas to point me in the right direction?

Thanks,

Brian