During one of my installations of Exchange Server 2013 I ran into a problem. I was using an old test VM with Windows Server 2012 installed on it and ran the power shell command to prepare the Schema and it returned the following error code:
Setup encountered a problem while validating the state of Active Directory; The supplied credential for ‘domainname\administrator’ operation is invalid
Simple fix; Just reset the Administrator users password and reboot the server.
