The domain join cannot be completed because the SID of the domain you attempted to join was identical to the SID of this machine

Just ran into this problem after copying around some VMs. The fix is a simple one, just run this command:

c:\Windows\System32\Sysprep>Sysprep /generalize /shutdown /oobe

It will take a while to run and you will need to re-enter your product key, but you will be able to join the domain when it is  complete.