samba nt_pdc

[Som Bunnet]

Hi! 
I am a Samba user.I have got a problem with using Samba as Nt PDC. The follow is my problem: 
I successfully joined the Samba controlled domain, but now I can't login! 
This is the window message: 
Window cannot connect to the domain, either because the domain controller is down or otherwise unavailable or because your computer account was not found............. 

Please help! 
Thank