Since we put in Exchange 2013 in July 2013 we have had a problem with Shared Calendars. Even though a User has Owner Permission on another Calendar, New Appointment is Grayed Out and the User cannot add or amend and occasionally Outlook will hang. We have tried Outlook 2010 and 2013 Clients as well as Cached Mode and Online Access. Exchange Server Standard 2013 CU2 was installed and this seemed to stop the problem for a while and now it has returned.
Permissions have been removed and reapplied both through the Exchange Powershell Interface and on the Mailbox. All other aspects of the system seem fine.
Any advice would be welcome.