Error (like this):
Adprep encountered a Win32 error.
Error code: 0x5 Error message: Access is denied.
HRESULT = 0x80070005
NT BUILD: 14393
NT BUILD: 2636
I was able to fix by going into Component Services on 2003 server, right click ‘my computer’, properties, on ‘default properties’ tab ‘enable distributed COM on this computer’ was unchecked. I checked it and reboot both servers, I was then able to promote the 2012 server to DC, adprep went thru with no issues.
update: the 2016 server can be 2012 or 2012R2 …