samba - May 2002 - Fail to join win2k to a NT domain where samba serves as a PDC

Dear sirs(madams):
  I've just configured samba 2.2.2 on FreeBSD 4.5 to server as a windows NT 
PDC. The domain once worked well after configuration. But today, I suddently 
encountered with certain trouble, that I can't join any clients to the 
domain any more. Even those I've joined to the domain sucessfully other days
can't be joined to the domain either after I removed them and tried to 
rejoin them. All the clients run win2k, and I've add the machine trust 
accounts mannually to the samba server. Things go like this:
  I logged in a win2k as administrator and configure the machine to join the 
intended domain. When asked to input the account and correspondent password 
having the authority to join the client to the domain, I input "root"
and
the password. Then the the following error message appears in a messege box:
      The folling error occured attempting to join to domain "301IAN"!
      Access Denied!
  I don't know what's going wrong. I've once used the same root
account to
join 2 lients to the domain successfully, and both of them still worked well 
in the domain even after such trouble happened. How can I shoot this 
trouble?

Thanks in advance!

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