When upgrading from 5.0.9 to 5.0.10, some users got an error message
Code:
The Zimbra Addin has experienced a serious error. Try restarting Outlook again.
Those were users who also had certain items not sync in the past, getting "Local Failure Notices".
I think this may have been in relation to Bug 32309.
Today, server and the affected clients were upgraded to 5.0.11 but the issue still exists!