Hi Zhen,
Have you tried re-entering the password into the configuration? Only reason I ask is that I have had similar experiences when pasting a password into the password fields. It populates the field, but actually keeps locking the account out.
It may be worth a shot? Another thing I would look for is the correct entry on the "Login DN" for the account you are using
It may be worth presenting your LDAP account unit config so we can take a look.
From what you have said the account you are using is a domain admin?
Regards
Mark