One of my employees is unable to access our shared mailbox. We added them from the admin center but when clicking on the new mailbox, after loading for a while, this error message appears:
"Cannot expand the folder. This set of folders cannot be opened. C:\Users\(our domain)\AppData\Local\Microsoft\Outlook\(employee email)\.ost is in use and cannot be accessed. Close any application that is using this file and then try again. You might need to restart your computer."