I renewed my lab and installed one Windows Server 2012 R2 in a VM. After that
I mad two machines from it. I promoted the first to a domain controller and
tried to domainjoin the second and the third. This failed saying that the SID is
the same as that of the domain controller.
The resolution is to sysprep the cloned machines.
Sysprep can be found under
Don’t forget to mark the "Generalize" Option
After the Reboot you have to redo the IP-settings of the NIC and
Domain join will work fine.