Why am I having trouble accessing a shared mailbox now?

If you were able to access the shared email or calendar before you migrated, it is possible that you are trying to access a mailbox that has not yet been moved to Office 365 Email & Calendar. We try to migrate groups and shared accounts at the same time, but sometimes we miss an account or can't move everyone on the same day. 

Please contact your local support desk so they can help identify and resolve the issue.