I was at a customer site whose Exchange admin was confused with the error message, while trying to upgrade from Exchange 2010 SP1 UR6 to SP2.
While trying to upgrade Exchange 2010 SP1 UR6 server to SP2, the following error comes up.
"Error: The Active Directory Schema is not up-to-date and Ldifde.exe is not installed on this computer. You must install Ldifde.exe by running Add-WindowsFeature “RSAT –ADDS”.
The exchange admin was confused as the SP1 installation was carried out successfully. Hence, the machine was/is capable of updating the schema.
The issue was that the Exchange 2010 SP1 install was done first on a different Exchange server and hence this server (the one that complains) doesn’t have the AD admin tools installed. That is exactly what the error message was saying as well.
After installing the AD admin tools and restarting the server, schema update and 2010 Sp2 setup was completed successfully.