As per Microsoft Active Directory architecture, every object (users, groups & computers) in the domain has a unique identifier, known as a SID. These SIDs are unique alphanumeric strings that correspond to a single object in the domain. When you copy a virtual machine directory, the resultant virtual machine has the same SID as the original virtual machine. When you try joining this new virtual machine to the same domain where the original virtual machine is, Active Directory sees two machines with a single SID and warns you that there is a SID conflict.
The solution? To change the SID of course!
You can use the Sysinternals PsGetSid tool to view a machine’s SID by running it with no command-line arguments.
To reset the SID please use:
sysprep /oobe /generalize
It can be found in the \Windows\System32\sysprep folder
The /generalize option instructs Sysprep to remove system-specific data from the Windows installation. System-specific information includes event logs, unique security IDs (SIDs), and other unique information. After the unique system information is removed, the computer shuts down. The /oobe option instructs the Windows installation to run Windows Welcome the next time the computer boots.
Sysprep must be used only to configure new installations of Windows. You can run Sysprep as many times as required to build and to configure your installation of Windows. However, you can reset Windows activation only up to three times. You must not use Sysprep to reconfigure an existing installation of Windows that has already been deployed. Use Sysprep only to configure new installations of Windows.
The clock for activation begins its countdown the first time Windows starts. You can use Sysprep for a maximum of three times to reset the clock for Windows Product Activation. After the third time you run Sysprep, the clock can no longer be reset.