problem with zone delegation (NS)

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Hello,
I have a dns (server A) (bind 9) which is master for the zone "gie.com" and
a second dns (server B)which is master for the zone "ad.gie.com".
So, to create the delegation for the zone ad.gie.com, i have this config in
the file zone gie.com.db (on server A):

File for the gie.com zone:

$TTL 86400
@       IN      SOA     SERVERA.toto.intra. root.toto.intra. (
                                            OPTIONS
                                         ) ; minimum

                        IN      NS      SERVERA.toto.intra.    ->primary
server for the zone gie.com
                        IN      NS      SERVERC.toto.intra.    ->secondary
server for the zone gie.com

ad                    IN      NS      SERVERB.ad.gie.com.    ->delegation
for the zone ad.gie.com

SERVERB.ad.               IN      A       10.52.100.22

test                 IN      A    10.10.10.10


When i request the dns (ServerA) with nslookup:
- for test.gie.com, it's ok
- for www.ad.gie.com, i have an answer "*** SERVERA.toto.intra doesn't find
www.ad.gie.com : Non-existent domain"

but when i request directely the server B for www.ad.gie.com, it's ok...

I don't understand the problem!
Thanks for your help...
Vincent