SYMPTOMS
After you change the domain name of the primary domain controller (PDC)
in Control Panel Network and then attempt to change the domain name of
the backup domain controller (BDC), the following error message appears:
You already have a connection to the domain. You must disconnect
before joining the domain.
When you attempt to use the previous domain name for the PDC, the
following error message appears:
The domain name entered is already in use by another computer.