Our only one existing dc is on a 2008 server. I just set up a new 2008 R2 and wanted to add it to this domain using dcpromo.exe. But I got an error saying I have to run adprep.exe /forestprep. Okay, it thought I just went ahead run it on the 2008 R2 but I got another error saying I have to run adprep.exe on a DC. Okay, then I have to run adprep.exe on the 2008 server as it is only one dc at this moment. But question to you, which version of adprep.exe should I use? Should I use the one from 2008 R2 or from the existing 2008 server's ? Please help.