On my Windows-XP PC, i see this, and ask mself why i get the 'Server:UnKnown'

D:\>nslookup 192.168.178.250
*** Can't find server name for address 192.168.178.250: Server failed
*** Default servers are not available
Server: UnKnown
Address: 192.168.178.250

*** UnKnown can't find 192.168.178.250: Server failed

D:\>nslookup opensuse
*** Can't find server name for address 192.168.178.250: Server failed
*** Default servers are not available
Server: UnKnown
Address: 192.168.178.250

Name: opensuse.example.com
Address: 192.168.178.250


D:\>nslookup -debug
------------
Got answer:
HEADER:
opcode = QUERY, id = 1, rcode = SERVFAIL
header flags: response, want recursion, recursion avail.
questions = 1, answers = 0, authority records = 0, additional = 0

QUESTIONS:
250.178.168.192.in-addr.arpa, type = PTR, class = IN

------------
*** Can't find server name for address 192.168.178.250: Server failed
*** Default servers are not available
Default Server: UnKnown
Address: 192.168.178.250

>



zone-file contains:
example.com. IN NS opensuse.example.com.
opensuse IN A 192.168.178.250

reverse-file contains:
.178.168.192.in-addr.arpa IN NS opensuse.example.com.
250.178.168.192.in-addr.arpa IN PTR opensuse.example.com.

Post your entire named.conf and the full contents of both zone files.

== named.conf ==
options {
directory "/var/lib/named";
# include "/etc/named.d/forwarders.conf";
};
logging {
category queries { log_file; };
category xfer-in { log_file; };
category xfer-out { log_file; };
category default { log_file; };
channel log_file { file "/var/log/dns.log" size 2048M; };
};
zone "localhost" in {
type master;
file "localhost.zone";
};
zone "0.0.127.in-addr.arpa" in {
type master;
file "127.0.0.zone";
};
zone "example.com" in {
allow-transfer { localhost; localnets; };
file "master/example.com";
type master;
};
zone "178.168.192.in-addr.arpa" in {
allow-transfer { localhost; localnets; };
file "master/178.168.192.in-addr.arpa";
type master;
};



== example.com
$TTL 2d
@ IN SOA opensuse.example.com. root.opensuse.example.com. (
2008082201 ; serial
3h ; refresh
1h ; retry
1w ; expiry
1d ) ; minimum

example.com. IN NS opensuse.example.com.
example.com. IN MX 10 opensuse.example.com.
opensuse IN A 192.168.178.250
asus IN A 192.168.178.2
router IN A 192.168.178.1
medion IN A 192.168.178.30
xppro1 IN A 192.168.178.50


== 178.168.192.in-addr.arpa
$TTL 2d
@ IN SOA opensuse.example.com. root.example.com. (
2008082200 ; serial
3h ; refresh
1h ; retry
1w ; expiry
1d ) ; minimum

.178.168.192.in-addr.arpa IN NS opensuse.example.com.
250.178.168.192.in-addr.arpa IN PTR opensuse.example.com.
1.178.168.192.in-addr.arpa IN PTR router.example.com.
2.178.168.192.in-addr.arpa IN PTR asus.example.com.
30.178.168.192.in-addr.arpa IN PTR medion.example.com.
50.178.168.192.in-addr.arpa IN PTR xppro1.example.com.

remove the leading period from .172...

I usually only use the last octet in reverse zones, i.e.
250
1
2
...

instead of fully-qualified, but I believe you need the trailing dot after "in-addr.arpa" if you put the fully-qualified address on the left.

You can do to see if named is generating any errors when it tries to load.

Yes, it works with changing thes few dots.....
(i MUST have read the manual in a wrong way

== 178.168.192.in-addr.arpa
and you're right about the fact that this:
is equivalent to: