When planning to deploy Exchange 2010 RTM Schema in an Exchange 2007 environment that is running SP3, you will encounter the following error:
“Setup encountered a problem while validating the state of Active Directory. The Active Directory schema version (14625) is higher than the Setup’s version (14622). Therefore, PrepareSchema can’t be executed.”
This is becasue the schema version of Exchange 2007 SP3 is higher than the one from the Exchange 2010 RTM setup.
Exchange 2007 SP3 already has the schema changes required by Exchange 2010, so you don’t need to perform E2010 prepareschema again. Please remember, that you still need to run setup.com /PrepareAD from Exchange 2010 setup.