Folder Doesn't Exist: A folder in the Destination mailbox was present at the beginning of the migration (either because it already existed or because it was created by the migration process) but is no longer available, preventing content from being migrated. This may happen because a folder was moved, deleted, renamed, or because permissions were changed.
Resolution:
Review recent folder changes and restart the migration. MigrationWiz will recreate the folder if it is not present at the Destination.