I must start with the easy question of are the two servers named the same? of course that is a dumb question but I have to ask it first.
if not then were these two DC’s created using an image file?
imaging is great to get servers up and running fast but one thing that you have to remember after imaging a system is to run a program like NewSID to create a new unique identifier for that system. even if you rename the computer it still keeps it’s original SID and that could be conflicting with the original DC.