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My 2nd DC is Win 2008 standard so I had to lower the functional level of my DC1 to 2008 Standard. After doing this, I still cannot join the 2nd DC to the domain.

The error I get is: The functional level of the domain or forst is incompatible with this operating system."

"The version of the OS installed is incompatible with the current domain functional level. You must upgrade to a new version of the OS before this server can become a DC in this domain".

"This error can occur if you have no been granted necessary permissions to read the data in the directory. For more info, please see 936241 in MS Knowledge Base."

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Functional levels cannot move down, only up (Edit: 2008R2 -> 2008 is an exception, provided AD Recycle Bin is not enabled; see below and here) - unless you restored all of your domain controllers to a point in time before the functional level was moved up, you didn't revert the change.

Verify your domain and forest functional level with the Domains and Trusts snap-in.

share|improve this answer… I followed these guides and it worked. According to MS you can go down to 2008 standard. Or perhaps I'm not understanding. – EagerToLearn Jul 6 '11 at 14:54
@EagerToLearn Good info; nice of them to allow rollback if recycle bin isn't enabled. Anyway, do check the domain level in Domains and Trusts; the article you linked covers only forest level, not domain level. (to roll back, Set-ADDomainMode -Identity -DomainMode Windows2008Domain) – Shane Madden Jul 6 '11 at 15:01
You're right, it's still at 2008 on the domain level, but I did successfully change it to 2008 Standard on the forest level. Can I do it on the domain level? – EagerToLearn Jul 6 '11 at 15:01
@EagerToLearn The powershell command I included will downgrade the Domain level. – Shane Madden Jul 6 '11 at 15:03
Ok cool, I'll give it a shot. Thanks man! – EagerToLearn Jul 6 '11 at 15:03

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