We are currently working on moving from Windows 2012 R2 as the DC to Windows 2019. We're running both of these machines on VMware ESXi 7. When I try to add the 2019 server as a domain controller, I receive the error message:
"Verification of replica failed. The forest functional level is not supported. To install a Windows Server 2019 domain or domain controller, the forest functional level must be Windows Server 2008 or higher."
I then ran Get-ADForest on the 2012 domain controller, and the output for ForestMode is "Windows2003Forest." So, I popped the Windows 2012 R2 iso into the virtual drive to run ADprep /forestprep, but I get a message that says Forest-wide information has already been updated, and it didn't attempt to rerun.
So, I'm at a loss at this point. Is there a way to force forestprep to rerun?
If you have no Windows Server 2003 domain controllers, you can raise the domain and forest functional levels.