The new cross domain planning functionality for Group Policy, RSOP Planning Mode, requires file system and Active Directory ...

The new cross domain planning functionality for Group Policy, RSOP Planning  Mode, requires file system and Active Directory Domain Services permissions  to be updated for existing Group Policy Objects (GPOs). You can enable this  functionality at any time by running "adprep.exe /domainprep /gpprep" on the Active Directory Domain Controller that holds the infrastructure operations  master role.  This operation will cause all GPOs located in the policies folder of the  SYSVOL to be replicated once between the AD DCs in this domain.  Microsoft recommends reading KB Q324392, particularly if you have a large  number of Group policy Objects.