The person who sent you the invitation will need to remove your permissions and then send a new invitation.If you've been granted permissions to edit a calendar, you won't be able to edit or add items immediately after accepting.If a user sets permission levels only to allow free/busy or free/busy limited details, an Outlook 2011 user will not be able to see any details of the shared calendar.PC users must grant "full details" to the Outlook 2011 user.
Basic free/busy time viewing is only viewable via the Outlook 2011 Scheduling Assistant feature, or via OWA.
I had her give me permissions to her calendar and when I had her assistant make a new meeting request it showed on mine and her assistants however never showed on the primary persons calendar unless we closed outlook and reopened it.
We do have cache mode enabled on all user mailboxes in the organization so that it will allow them to work in outlook right away without it taking so long to load.
We're currently investigating how to enable instant syncing in these situations.
When accepting a shared calendar, you might see an HTTP 500 error. If you see the error more than once, contact Support.