When you want to virtualize a domain controller there are some things that you should not do. For example, you shouldn't make copies of vhds that belong to domain controllers and then start those vhds in virtual machines. Why? Well, you can cause replication issues. To learn more about the Active Directory team recommendations for running domain controllers in virtual environments, see Running Domain Controllers in Hyper-V at http://technet.microsoft.com/en-us/library/dd363553.aspx
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