I tried finding relevant items in the bug tracker but failed.
*User A has shared several calendars with User B, some read only some manager level. Everything is fine from webclient.
*User A sets up caldav to their account and uses iCal to add tasks on the calendar. User A has no particular interest in User B seeing those tasks, but wants the events connected to the various calendars.
*User B sets up caldav to their account on server. The delegated calendars come across fine, including all the appointments.
*During a subsequent automatic refresh, User B gets errors that they do not have permission to see the tasks in the shared calendars and is given choice of going offline or 'reverting to server'. User B has to select go offline to not get further messages.
I don't expect our site to upgrade the server to 6.X until next May although maybe this winter break. Does anyone have any suggestions? Best work around so far is subscribe to the individual calendars as read only using the ics links, iCal gives the option of ignoring the todos.