The MailboxTrackingFolder entity represents a tracking rule to map a Microsoft Exchange inbox folder to a Microsoft Dynamics CRM entity record and was introduced with the release of CRM 2015 V7.1
If you had any CRM solution installed on CRM 2015 V7.0 and now CRM is upgraded to V7.1, importing same solution for V7.1 will bring up an error message that includes the text “MailboxTrackingFolders” associated with a customised entity.
While one will expect Microsoft to automatically handle the additional entity linked to customized entity, currently Microsoft only points to the error and flag the import of the solution as failed.
To overcome the issue, delete the currently installed solution and import the updated solution for V7.1
NOTE: If your solution is Dynamics Docs, you need to download the templates firs (Settings>Docs Templates>Edit Download Template) as they will be removed when the solution is removed.