OS X :: ICal Exchange Shared Calendar

One of my customers is experiencing an error with one particular Exchange 2007 shared calendar in iCal. The shared calendar he has access to is in the Delegation tab of the Exchange account as Read Only, which is his correct level of access. The calendar will initially load correctly, but over time it starts to display an error with recurring events similar to this -- "iCal can't save the event "office time - do not disturb" to the exchange server. The account can't be modified. To discard your changes and continue using the version of your calendars that's on the server, click Revert to Server. To save your changes on your computer until the problem is resolved. click Go Offline." After selecting both Go Offline or Revert to Server, it cycles through all the recurring events on an infinite loop. If you select Go Offline, the errors will stop, but taking the account back online to get calendar updates will result in the error immediately returning. Removing and re-adding the account in the delegation tab will refresh the calendar without error for a short period of time, but the errors will eventually pop up again.