For updated information and a link to download a patch for this issue, please see the UPDATE: Patch available for ArcGIS 10 Geodatabase issue with synchronizing replicas blog post.
Esri is working on a fix that should be available soon. For updates on status, you can use bug number NIM058231 — Upgrading geodatabases with replicas to version 10 causes synchronization process to fail.
We will keep you posted via this blog as updates become available.
Mike H., Program Manager
User Advocacy Group, Esri Support Services