Installation of Exchange 2010 on Windows 2008 R2 is pretty cool but sometime it can make you crazy. There could be situation that you have removed computer account before and not delete stale computer object from AD. You may get below error message when you launch exchange 2010 setup on windows 2008 R2 machine.
To resolve this problem, You must remove computer account from domain and rejoin it, Wait for some time for replication and then start installation of Exchange. It will go pretty smooth 🙂