I have configured 2 User Profile Service instance's on a SharePoint 2010 farm to cater for an Intranet and Extranet Domain. One UPS runs on the app server and hosts the Intranet sync and the other runs on the extranet server hosting the extranet sync. Both servers have the User Profile Service and User Profile Synchronization Service running.
We have noticed that sometimes the Incremental Sync job for the Intranet is actually running on the extranet server and reports the following error in the 'Failed Timer Job' list in central admin - The RPC server is unavailable. (Exception from HRESULT: 0x800706BA)
The current SharePoint patch level (build version) for each environment is 14.0.6120.5006 (SharePoint 2010 Server with SP1 and April 2012 CU applied).
Any help would be appreciated.