This error can occur if your device crashes at some point while writing to the app's database.
If this happens, chances are that there will be no way to fix this and save your data...
If by any chance the part of the database that is corrupted is NOT the data, but the indexes (a way to quickly access the information), then you can go to Settings/About and use the 'Repair Database' option.
If that doesn't help, you will have to clear the app data and start over...
If you've logged into the app before, then your database has been saved to the cloud. So logging back in will allow you to restore the data BUT only proceed if you are sure that the backup was made before the corruption happened, otherwise you will be restoring the same corrupted database...