I recently ran into a problem with an RC installation of Windows Server 2012 (in a VM). When I tried to add it as a domain controller in an existing domain, an error was displayed that the server didn't have enough storage space to process the command.
What's one fix? Increase the amount of RAM. In this case, the VM had 1.5GB of RAM. I bumped it up to 4GB of RAM and the promotion to a domain controller was successful!