Tonight I’m trying to promote a spanking new Windows 2008 R2 server as a domain controller in an existing Windows 2003 AD.  When I ran dcpromo on the new server I was presented with the following message from the Active Directory Domain Services Installation Wizard, “To install a domain controller into this Active Directory forest, you must first prepare the forest using “adprep /forestprep”.  The Adprep utility is available on the Windows Server 2008 R2 installation media in the supportadprep folder.”

I promptly opened and Command Prompt on the R2 server, navigated to the supportadprep folder and ran adprep /forestprep.  No joy!  Now I got the message:

Adprep cannot run on this platform because it is not an Active Directory Domain Controller.
[Status/Consequence]
Adprep stopped without making any changes.
[User Action]
Run Adprep on a Active Directory Domain Controller.

So, I went to one of my 2003 domain controllers and ran adprep /forestprep.  Another problem!

The image file C:supportadprepadprep.exe is valid, but is for a machine type other than the current machine.

It took a few minutes but I finally figured out I need to run adprep32 /forestprep since my 2003 server is 32 bit.  Ah, hah!  Of course, there’s this little message:

ADPREP WARNING:
Before running adprep, all Windows 2000 Active Directory Domain Controllers in the forest should be upgraded to Windows 2000 Service Pack 4 (SP4) or later.
[User Action]
If ALL your existing Windows 2000 Active Directory Domain Controllers meet this requirement, type C and then press ENTER to continue. Otherwise, type any other key and press ENTER to quit.

Just a little bit more….

From the same 2003 server you’ll have to run adprep32 /domainprep as well.

Now that adprep(32) /forestprep  and adprep(32) /domainprep were successfull I can promote my 2008 R2 server to DC.