Hello list, I've done some more investigations

and it looks like the secondary (slaves) servers
are refusing the zone change :

0.000000 ns0nsserver.domain.fr -> ns1nsserver.domain.fr DNS Zone change notification SOA domain.fr
0.030909 ns1nsserver.domain.fr -> ns0nsserver.domain.fr DNS Zone change notification response, Refused

Any idea why is this happening ??