DCPromo will tell you that the Forest has not been prepared for the version of Windows you are trying to promote (ie, R2).  This would normally not be a problem, the R2 media contains an adprep.exe to update the schema for R2 Domain Controllers.

Of course if you take your new 64-bit R2 disc 2 media and try to run adprep on the 64-bit server you will receive this error:

C:\WINDOWS\CMPNENTS\R2\ADPREP>adprep /forestprep
Adprep cannot run on this platform because it is not a domain controller.
[Status/Consequence]
Adprep stopped without making any changes.
[User Action]
Run Adprep on a domain controller.

Makes sense, so of course you put the disc into your existing Domain Controller and run adprep again.

Z:\>adprep /forestprep
The image file Z:\ADPREP.EXE is valid, but is for a machine type other than the
current machine.

Thats right, you can’t use your 64-bit media to run adprep on a 32-bit Domain Controller.  This is where the chicken and egg scenario kicks in – how do you get your 64-bit R2 server to be a Domain Controller with no pre-existing 64-bit or R2 Domain Controllers available for the required schema update?  Its not like Microsoft ships you a 32-bit copy of the OS when you buy the 64-bit edition.

The solution is to get your hands on the 32-bit R2 media.  If you don’t have a friend or colleague with a copy the next easiest way to get it is from the trial software downloads on Microsoft.com.  Go here and jump through the ridiculous hoops to “buy” a $0.00 trial edition so that you can download the ISO files.  You only need to download and burn the ISO for disc 2 which contains the R2 adprep.exe and schema files.

Update: you can also download this hotfix that contains only the R2 adprep files.

Related posts:

• Exchange 2007 ADPrep Error Executing Ldifde.exe to Import Schema File
• Security descriptor error during Exchange Server 2007 schema extension
• Installing Exchange Server 2007 pre-requisites on Windows Server 2008
• Exchange 2010 FAQ: Is Direct Exchange Migration from 2003 to 2010 Possible Without Upgrading to 2007?
• Exchange 2010 Setup Error – The Exchange Server is in an Inconsistent State

This article Windows Server 2003 32-bit R2 media needed to prep a non-R2 domain before first 64-bit R2 DC can be promoted is © 2009 ExchangeServerPro.com

Get more Exchange Server tips at ExchangeServerPro.com