During a DFSR sysvol migration on Windows Server 2008, problems can occur with the migration of Read Only Domain Controllers.
See the image below.
The RODC is stuck trying to move to the Prepared state. First go to the RODC and type Repadmin /SyncAll /AeD.
On the PDC Emulator, run dfsrmig /GetMigrationState.
If the migration completed, continue on. If not type dfsrmig /CreateGlobalObjects. This will manually create the global objects for DFS replication.
On the PDC Emulator, run dfsrmig /GetMigrationState. You should be ready to move on to the next step in the migration process.