The new b18 release has a new database integrity feature (described in the release notes – everyone should read them!) Each time a database is opened, Panorama checks it to see if it is damaged. If it is, you’ll see an error message and Panorama won’t open the database.
You mention “the dropbox copy”, which makes me think you are storing the database in your Dropbox folder. That may be the source of the damage. This could especially happen if a database has been modified on another computer and Dropbox hasn’t completely synchronized it yet.
You can disable the integrity check, which would allow you to open your database. Of course then you run the risk of Panorama not checking for damaged databases, which may cause other problems.
Do you mean Panorama X 10.1.2? If you are still using this older version, you should disable integrity checks. The latest b18 version saves an “integrity seal” as part of the database to allow it to detect virtually any kind of damage. But the older version doesn’t know anything about the integrity seal. If you use an older version after saving with the b18 version, the integrity seal won’t get updated when the older version makes changes. Then when you go back to the b18 version it will think the file is damaged, That’s another possibility for what caused your problem. Unless you have a very strong reason, I would recommend not using older versions of Panorama X once you have installed the b18 version. Just use only the b18 (or newer version) all the time.