On a user account that is experiencing this issue, I found in the user's Outlook folders a "Sync Issues" folder with a child called "Local Issues" that contained an item listing all the appointments that should have been synced and they all show the same error.
Code:
[Details: GITERROR! Failed to get OOM helper instance.]) id (1585) type(appointment) message([Subject: Server Migration]
What does that mean ?
ZCS NE 5.0.9, Outlook 2003 SP3 on Vista 32 bit, SP1 with ZCO 5.0.9