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Did you run the adprep /forestprep command on the original DC? &nbsp;It has to be done on the computer that is the schema master, which would be your existing DC. &nbsp;If so, then check the schema version to confirm that the adprep process worked. &nbsp;This article describes both how to run the adprep command and how to check that is has succeeded:<br />
<a href="http://technet.microsoft.com/en-us/library/cc773360.aspx" rel="ugc">http://technet.microsoft.com/en-us/library/cc773360.aspx</a>&nbsp;<br />

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p.s I know you already ran it from the CD but check the reg key and verify it is infact the same version that your domain is using.
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I am trying to promote an ADC (Server 2003R2 Box) to an existing domain that has a single DC. &nbsp;the PDC box is Server 2003 Ent. &nbsp;I have tried to do a forest prep / adprep to the server 2003 Ent box and it says its successful. &nbsp; When I then try to promote the ADC I get a failure msg of:<br />
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The opperation failed because the active directory installation wizard can not continue becasue the forest is not preped for intalling windows server 2003. &quot;&nbsp;The version of AD schema of the source forest is not compatible with the version of active directory on this computer.&quot;<br />
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PS. Domain and Forest levels are at server 2003 on existing PDC 2003 Ent. and the server 2003R2 Std disk 2 was used for AD Prep.
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I am trying to promote an ADC (Server 2003R2 Box) to an existing domain that has a single DC.  the PDC box is Server 2003 Ent.  I have tried to do a forest prep / adprep to the server 2003 Ent box and it says its successful.   When I then try to promote the ADC I get a failure msg of:

The opperation failed because the active directory installation wizard can not continue becasue the forest is not preped for intalling windows server 2003. " The version of AD schema of the source forest is not compatible with the version of active directory on this computer."

PS. Domain and Forest levels are at server 2003 on existing PDC 2003 Ent. and the server 2003R2 Std disk 2 was used for AD Prep.

Server 2003R2 STD fails DCPROMO for ADC in Server2003 Ent domain environment after successfull domain prep.

Windows Server 2003 was based on Windows XP and was released in four editions: Web, Standard, Enterprise and Datacenter. It also had derivative versions for clusters, storage and Microsoft’s Small Business Server. Important upgrades included integrating Internet Information Services (IIS), improvements to Active Directory (AD) and Group Policy (GP), and the migration to Automated System Recovery (ASR).