There seems to be a strange issue with Apples iCal using a Google Apps backend when you try to accept or deny invitations sent from Lotus Notes. The setup:
Calendar Client: iCal 4.0.4 on Mac OS 10.6.6
Server: Google Apps
Sync via CalDAV account in iCal
Invitation sent from Lotus Notes comes with an ICS attachment
Invitation will be displayed in iCal
User changes status in iCal by accepting or denying the invitation
iCal tries to sync back the changes to Google Apps
after half a minute sync stops with the failure message shown above. The process CalDAVWriteEntityQueueableOperation receives the message „HTTP/1.1 500 Server error code: f52e483e“ from Google Apps
Status in iCal and in Google Apps stays open
Only way to accept or deny the invitation is to do it in Google Apps Calendar web frontend directly. This syncs correctly back to iCal.
It seems there are some users out there experiencing the same issues. But no one found a solution yet. So is anybody aware of that problem and knows how to fix it?