Of course the error code came from Moses on a stone tablet that was dropped to us from a stork...
From Outlook's Send/Receive error window. And this from Outlook's OPMLog.log file:
2014.12.16 14:45:48 Top of Personal Folders: ReportStatus: RSF_COMPLETED, hr = 0xffffffff800c8100
2014.12.16 14:45:48 Top of Personal Folders: Synch operation completed
2014.12.16 14:45:48 Sending done, Error code = 0x800c8100
From Outlook's Send/Receive error window. And this from Outlook's OPMLog.log file:
2014.12.16 14:45:48 Top of Personal Folders: ReportStatus: RSF_COMPLETED, hr = 0xffffffff800c8100
2014.12.16 14:45:48 Top of Personal Folders: Synch operation completed
2014.12.16 14:45:48 Sending done, Error code = 0x800c8100