I saw this error message on Group Policy Management when I did a status check on the AD replication. All domain controllers were stuck with replication in progress with their respective Sysvol "inaccessible" against the PDC emulator. I couldn't find any error events on "DFS Replication" at all - the replication just got stuck in progress.
When this happens, follow the steps on How to perform an authoritative synchronization of DFSR-replicated SYSVOL.
