A simple delegation issue

[Storming Norman]

Where is the 'A' record to identify your sub-zone?
The zone should look similar to this:

@               IN SOA          ns.fhtw.        root.fhtw. (
                                        2005100103      ; serial
                                        3h              ; refresh
                                        1h              ; retry
                                        1d              ; expiry
                                        1d )            ; minimum

                                 IN    NS           ns.fhtw.
                                 IN    A             192.168.100.2
                                 IN    MX   0      wpc
 # not required obviously
wpc                           IN    A             192.169.100.2
ns                             IN    A              192.168.100.1

d01                           IN    NS            ns.d01.fhtw.
d01                           IN    A              192.168.100.4
ns                            IN     A              192.168.100.4