PhotoStructure uses a bunch of techniques to keep your library intact and valid, but unfortunately, power outages, software bugs, disk errors, and network errors can all take a toll on the integrity of a library.
PhotoStructure runs some validation on library databases on startup, and if those fail, it will ask you to try to recover from a library database backup.
If none of the backups work, you’ll want to restart your library from scratch.
Ah, good point, is forgot about the replica DB. V2.0 adds a file sanity check to make sure an older library copy isn’t used as a replica, but to be safe, you can delete /ps/tmp.