WSRV_Guru

The fact that the domain functional level is at 2008r2 would not make a difference, since Windows 2012r2 is supported at the functional level you've got set currently. I'd recommend taking a look at this TechNet article to further understand domain functional levels: https://technet.microsoft.com/en-gb/library/understanding-active-directory-functional-levels%28v=ws.10%29.aspx Do you just have the one DC or more? Also, do you know which DC is the primary controller?

Unless you have other servers attached to your domain that are are 2008 or below, I'd leave the domain functional level at 2008r2.

Hi CapnPugwash, Have you checked whether the operations master is set to the correct DC and that the FSMO roles are also hosted on the correct one too? You can check which DC is the operations master by heading over to Active Direcotry Domains and Trusts, right-clicking the Active Directory Domains and Trusts icon again and then pressing Operation Masters. Let me know the outcome.