iCal with OS X 10.5.2 sync errors

[nsmarler]

When synching one particular user's calendar into iCal from the ZCS server, the following message pops up:

(null) - May 27 2008 09:30 PM

This item could not be synced because you do not
have the required rights on the folder. To get back in
sync, you will need to do a reset sync.

However, doing a reset sync doesn't resolve the issue.

In the connector logs, we see this coinciding with a presentation of that error dialog:

[Wed May 28 16:14:02 200] <?xml version="1.0"?>
<soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope">
   <soap:Header>
       <context xmlns="urn:zimbra">
           <change token="548643"></change>
       </context>
   </soap:Header>
   <soap:Body>
       <soap:Fault>
           <soap:Code>
               <soap:Value>soap:Sender</soap:Value>
           </soap:Code>
           <soap:Reason>
               <soap:Text>permission denied: private appointment/task cannot be created on behalf of another user</soap:Text>
           </soap:Reason>
           <soap:Detail>
               <Error xmlns="urn:zimbra">
                   <Code>service.PERM_DENIED</Code>
                   <Trace>btpool0-1122:1212016241747:2e2d6e3be2f0df88</Trace>
               </Error>
           </soap:Detail>
       </soap:Fault>
   </soap:Body>
</soap:Envelope> (23049)
[Wed May 28 16:14:02 200] SOAP message error: service.PERM_DENIED:permission denied: private appointment/task cannot be created on behalf of another user (23049)
[Wed May 28 16:14:02 200] [assert] error: (null)
[assert] where: "ZimbraClient.mm", "-[ZimbraClient setAppointment:zid:rev:]", line: 1647
(23049)
[Wed May 28 16:14:02 200] [assert] error: !err
[assert] where: "AppointmentManager.mm", "-[ZimbraAppointmentManager applyChangesToServer:folderModifies:folderDeletes:itemCreates:itemModifies:itemDeletes:]", line: 4178
(23049)
[Wed May 28 16:14:03 200] committing changes (23049)
[Wed May 28 16:14:03 200] finished syncing (23049)

I notice the "PERM_DENIED: permission denied: private appointment/task cannot be created on behalf of another user" line. So, what's the next step in tracking these (null) items down? I don't see calendar events in either the synching user's iCal calendar for that date and time, nor are there any for the user whose calendar in ZCS is being synced.