[Samba] smbclient sometimes works but usually do not!!

[Gul Seda Unal]

hi all;
if u're able to join samba3rc1 to an ads domain help me with an answer!
i did everthing and tested so i'm sure that all works well accept 
SMBCLIENT!!!!			
[root at atolye4 root]# /usr/local/samba/bin/smbclient //160.75.5.51/unalgu 
-U unalgu -W CC
Password: 
tree connect failed: NT_STATUS_BAD_NETWORK_NAME
[root at atolye4 root]# /usr/local/samba/bin/smbclient //160.75.5.51/unalgu 
-U unalgu -W CC -k
tree connect failed: NT_STATUS_BAD_NETWORK_NAME
i tried both with and without Kerberos none worked.but after 10 or more 
times givin this error it works.it's a big mess!!
help me