reverse resolution failing

[Jim Pazarena]

my named is 9.9.0

while it can resolve "webmail.acrodex.com" ( 139.142.184.10 )

it cannot reverse resolve 139.142.184.10

(example follows).
However, if I do a simply nslookup using goodle DNS.
nslookup 139.142.184.10 8.8.8.8
IT WORKS!

Can anyone suggest where I may be going wrong with this?
my "dig" response follows.
Many thanks!

Jim

mail# dig -x 139.142.184.10

; <<>> DiG 9.9.0 <<>> -x 139.142.184.10
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 49017
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;10.184.142.139.in-addr.arpa.   IN      PTR

;; Query time: 125 msec
;; SERVER: 207.34.147.93#53(207.34.147.93)
;; WHEN: Thu Feb  7 09:30:12 2013
;; MSG SIZE  rcvd: 56

mail#