We have recently migrated Exchange from 2010 on premise to O365 in the cloud. We are able to access shared mailboxes through owa but the shared mailbox does not show in Outlook on the desktop. I can add the mailbox manually but it takes a minute or two for the process to complete and then when I try to open the shared mailbox I get this error..."Cannot expand the folder. The set of folders cannot be opened. The file D"\users\%username%\appdata\local\Microsoft\%email address% 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."
Any help is appreciated.