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Active Directory Installation

When I try to run the Active Directory Installation Wizard on a Microsoft Windows Server 2008 R2 server, the wizard does not finish, and you may receive the following error message: The Active Directory Installation Wizard cannot continue because the forest is not prepared for installing Windows Server 2008. Use the Adprep command-line tool to prepare both the forest and the domain. For more information about using the Adprep, see Active Directory Help.The version of the Active Directory schema of the source forest is not compatible with the version of Active Directory on this computer.
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Gabriel Clifton
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Have you ran the adprep.exe /forestprep command
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Yes / forestprep, /domainprep, /grpprep from th 2008 r2 media
Please post the results from the following command (edit to match your domain name):

repadmin /showattr * “cn=Schema,cn=Configuration,dc=EXAMPLE,dc=COM” /atts:ObjectVersion
If your current Schema Master is 2003 32-bit you'll need to use adprep32.exe and not adprep.exe.
You also need to ensure the account you are using is part of either the Enterprise Admins or Schema Admins group. I would also recommend you raise your Domain and Forest Function Levels to 2003 if you only have 2003 servers in your environment.

To check your current Domain Function Level, go into Active Directory Users and Computers > right click on your domain name on the left pane > Raise Domain Function Level (this won't actually raise the level just yet, we're just checking the current level) > look underneath Current domain functional level. This needs to be Windows 2000 native at a minimum.

To check your current Forest Functional Level, go into Active Directory Domains and Trusts (click StartAdministrative Tools) > right click on Active Directory Domains and Trusts in the window that appears > Raise Forest Functional Level (again this doesn't actually raise the level just yet) > look underneath Current forest functional level. This needs to be Windows 2000 at a minimum.