A. If the following error message is displayed when you attempt to add a computer running Windows NT to the domain:
"Unable to connect to the domain controller for this domain. Either the username or password entered is incorrect."
The error message is displayed even though networking is enabled and the correct administrator name and password credentials were supplied. The problem is that the PDC has SMB signing set to required and the client cannot communicate as it does not have SMB signing enabled.
Two options are possible. The first is to disable RequireSecuritySignature SMB signing on the domain controller as described in Q. How do I enable SMB signing? or install the machine into a workgroup, enable SMB signing then join the domain. Of course this would not work with BDC's.