When you upgrade from CRM 2011 to 2013, you will need to grant your users security permission to read the “Mailbox” entity. This is because in CRM 2013, the user’s mail preferences for incoming/outgoing mail are set on the mailbox entity and not on the user record (like they were in earlier versions). If you don’t grant read permission to mailbox entity, they won’t be able to configure CRM for Outlook.