Forest-wide information can only be updated on the Active Directory Domain Controller that holds the schema operations master ...

Forest-wide information can only be updated on the Active Directory Domain Controller that holds the schema operations master role.
[Status/Consequence]
Adprep has stopped on this Active Directory Domain Controller and must be run on the current schema operations master, which is %1.
[User Action] 
Log on to the %2 Active Directory Domain Controller, change to the directory of adprep.exe on the installation media, and then type the following command at the command prompt to complete the forest update: 
adprep.exe /forestprep