Usually occurs if the Information Store service goes down or if the Public Store is down or offline. User Action : Confirm that the Information Store service is running and that the Public Store is mounted.
The mailbox database was then re-created and the journal mailboxes moved back. Summary : something strange must have happened when the original mailbox database was created.
Not the technical solution that some would want, but hey, it fixed it nonetheless!
I eliminated the error by stopping Exchange System Attendant and its dependent services, then restarting SA and each dependency individually.
MS Exchange Free Busy Publish then initialized properly. Clicking on the link in the 8197 log entry, I found a suggestion from Microsoft to restart the System Attendant service.